Tree peony, originated from China, is one of the famous flowers in China and the central plains have always been the center for cultivating tree peonies. Cultivar Group of Tree Peony from Central Plains of China, which owns the most cultivars resources, has the longest history among all the cultivar groups. There were many researches on its cultivation and physiology, but a few on its genetic diversity, while the genetic diversity has not been revealed thoroughly. Since all the cultivars, which had not been screened by any modes, were preserved in the germplasm nursery gardens, not only farming land had been wasted but also the further studies and the effective applications been hindered. The studies on the construction of a core collection of Chinese tree peony cultivars and on its application will be an effective method to solve the problems above. According to the spot investigation and the descriptions in Pictorial Record of Chinese Tree Peony Varieties, genetic diversity and methodology establishing a core collection of the 400 tree peony cultivars from central plains were studied by combining the phenotypic data with the molecular data gained by ISSR and/or AFLP. The main results were as follows:1. Phenotypic database of 400 cultivars and the molecular database of the 120 cultivars in the primary core collection were firstly gained.2. Shannon index of the accessions was 0.9966 by analyzing on the phenotype genetic diversity. Shannon index for Single-flower section and Proliferate-flower section were 0.9688 and 0.8599, respectively. Among the 10 floral forms, Shannon index of crown form was the highest (0.9100), golden circle form, the lowest (0.313). The phenotypic traits, such as the length of leaf stalk, vertical and horizontal diameters of flower, leaf and flower color, were with higher Shannon index (>1) , while the Shannon indexes of other traitswere relatively lower. It was suggested that the genetic diversity of Chinese Central Plain Tree peony Cultivar Group should be enriched further.3. The sampling strategies to establish a core collection was firstly studied based the morphological database from the phenotypic traits of the 400 cultivars. The optimal methodology was that the primary core collection, which contained 30% samples of the accessions, should be constructed by means of defining the sampling number within each section by square root and drawing the samples by UPGMA cluster after grouping the accessions by floral form; the Core contained 15% samples of the accessions should be established at last based on minimizing the samples in the primary core by clustering to the phenotypic and molecular data.4. A primary core collection with 120 tree peony cultivars was constructed according to the optimal sampling strategy gained by our research. All the traits and component types of the primary core collection was the same as accessions according to the phenotypic analysis. The representation of Shannon index of the primary core collection to the one of accessions reached 99.12%. There were no significant differences on Shannon diversity indexes of the phenotypic traits between the primary core collection and accessions.5. A steady ISSR and AFLP reaction volumes were established based on the genomic DNA of all the 120 tree peony cultivars in the primary core collection. 244 DNA bands were amplified by 8 ISSR primers screened out from 83 ones, and 231 DNA bands (93.3%) among them were polymorphic. Mean of the PIC values of the 8 primers was 0.44. 1162 DNA bands were amplified by 8 AFLP pair primers screened out from 64 ones, and 1152 DNA bands (97.6%) among them were polymorphic. Mean of the PIC values of the 8 pair primers was 0.67. The rich genetic diversity of the primary core collection was proved further by the result of ISSR and AFLP markers.6. The Core composed of 60 cultivars was firstly established by the method of "phenotypic data + AFLP data + ISSR data", which had no significant difference with the primary core collection both on the phenotypic and DNA levels. Compared to the accessions, all the test indexes and the average genetic distance between the cultivars of the core collection were higher, and the 15% samples of the accessions were retained, aswell the RPR was 99% to the accessions.