As one of those frontier subjects in the field of photographic science, photothermographic materials (PTG materials) have attracted many attentions for their various advantages, such as excellent imaging quality, steady image preservation, convenient operation and pollution-free dry technology. Although traditional silver halide film market has been shrinking severely in recent years, PTG materials have showed its bright future. Since understandings about the detail of the relevant imaging process would be the key for deeper researches, scholars in this field have made great efforts in order to reveal the concerning mechanism; among them, Whitcomb and Maekawa have the very important silver ion transfer and reduction process thoroughly investigated and analyzed, but raised quite different proposals.In current study, using phthalic acid (PA) and phthalazine (PHZ) as the starting materials, di-silver phthalate (Ag2PA) and complex [Ag2PHZ2PA·H2O], which were supposed to be the silver-intermediates in the development process, were prepared using liquid deposition approach; their compositions and structures were carefully characterized through methods of ICP-AES, elemental analysis, XRD, FTIR, TG and DSC. The analysis of silver ion transfer in development process for PTG materials showed that the toners PA and PHZ could have the reaction course changed and the activation energy reduced, and the silver ion transfer course proposed by Maekawa seemed to be reliable in some extent.Using X-ray powder diffraction (K value) method, the solid state reaction between silver behenate (AgBeh) and PA was studied within the developing temperature of PTG materials ranged from 100℃to 123℃. The obtained data showed that this reaction was actually diffusion-controlled, and Jander equation could properly describe this reaction in a certain reaction time course. The apparent activation energy and apparent frequency factor of the solid state reaction were 84.5 kJ·mol-1 and 7.06×107 min-1, respectively. Diminishing the granularity of AgBeh and PA could speed up the progress of development. XRD and FTIR results proved that the reaction between Ag2PA and PHZ was controlled by the diffusion of the reactants.The diffusion behavior of PA, PHZ and 6-isopropyl phthalazine in binder PVA were measured, and the diffusion coefficients for PHZ and 6-isopropyl phthalazine were found to be larger than that of PA. It could be seen that the values of the above mentioned diffusion coefficients would be increased if raising the diffusion temperature. For each of the following systems, such as PA—PVA, PHZ—PVA and 6-isopropyl phthalazine—PVA, the values of the diffusion coefficients would become smaller with the increase of the binder concentration under different temperatures. For PA—PHZ co-toner system, the main factor of controlling the silver ion transfer velocity was the diffusion behavior of PA in the binder coat. Several technical improvements, such as increasing the development temperature, shortening the diffusion distance of PA in the binder coat by adjusting the coat structure and ingredients, decreasing the binder concentration, were all advantageous for enhancing the development velocity. For PA—6-isopropyl phthalazine co-toner system, the diffusion behavior of 6-isopropyl phthalazine in the binder coat would limit the silver ion transfer velocity, therefore be propitious to obtain a better silver image.The diffusion coefficients of toners PA and 6-isopropyl phthalazine in the binder styrene-butyl acrylate latex were also measured, and the diffusion activation energies of PA and 6-isopropyl phthalazine were determined. The experimental data showed that the diffusion coefficients of PA and 6-isopropyl phthalazine in styrene-butyl acrylate latex were greater than those of PA and 6-isopropyl phthalazine in PVA under the same binder concentration.