It is well known that nitrogen is one of the most common impurities in industry and natural diamond. In natural diamond the concentration of nitrogen is commonly about 2×103 ppm, mostly colorless (type Ia), but the synthetic diamond is only about 300ppm, yellow (type Ib). There are so significant differences in nitrogen concentration and form between the two type diamond. It cause a lot of differences in properties. Syntheses of diamond with a high concentration of nitrogen in laboratory provide a means for fabricating diamond with nitrogen concentration and form similar to those of the natural diamond and for fabricating diamond with "boron skin and nitrogen core". Furthermore, these can provide new knowledge of mechanisms for natural diamond nucleation and growth. It should be helpful for future study toward the understanding of how nitrogen atoms accommodate themselves in the synthetic diamond, and how high concentrations of nitrogen eventually become platelets or tetrahedron in the natural diamond. In our previous studies, using powder catalyst and NaN3 as an addition, we have already synthesized industrial diamond with a considerable nitrogen content of natural diamond. However, industrial-grade diamond particulate\'s size is limited, and the general size is only about 0.5mm. There is still a distance with natural diamonds. In addition due to the smaller size also limits the applications of high nitrogen content diamonds. Therefore, it is very important to study on high nitrogen content diamond synthesis in HPHT condition.In this study, we use a cubic anvil HPHT apparatus. Using catalysts (FeNiMnCo, FeNiCo), graphite and addition of NaN3, large green single crystal diamond with high nitrogen concentration is firstly synthesized by temperature gradient method. We have studied the NaN3 effect on the nitrogen contents and growth of gem diamond.In order to further study the impact of the addition of NaN3 to crystal growth, we used SEM to study the surface morphology of crystals. With the addition of NaN3, crystal gradually changed to (111) crystal plane rich patterns, at the same time the crystal surface became more and more smooth, rarely occurred defects such as melt pit. When the addition of NaN3 further improved, the crystal surface began to appear a series of parallel grooves. As the addition of NaN3 reached 0.6wt%, the crystal surface was irregularly distributed lots of triangular pits and irregular-shaped steps.Above all, through the research on high nitrogen content gem diamond synthesis, we found a effective means to synthesize high-quality high-nitrogen diamond. synthetic crystals reached the maximum nitrogen content 1707ppm.