The characteristics of Mn-Ni rapid solidified powder catalyst (MNRSPC) and theprocesses in synthesizing diamonds using this catalyst were studied by means of optical microscope, X-ray diffractometer, SEM and TEM. The change of temperature and pressure during the diamond synthesis was analysed in the systems of powder catalyst and flaky catalyst.The Physical and chemical characteristics of MNRSPC were investigated. The results show that, first, this powder catalyst has high surface energy, high nonequilibrium carbon content, lower melting point than that of domestic NiMnCo flaky catalyst; second, this powder catalyst has single face-centered cubic structure with lattice constant being 3.559A.The process parameters of the synthesis of MNRSPC on domestic cubic high pressure apparatus were studied for the first time. Using the optimum seeking method, the better process parameters for one-step,two-steps increasing pressure processes were determined, and the synthesis of diamond in the (?)23 synthesis cavity The characteristics of Mn-Ni rapid solidified powder catalyst (MNRSPC) and the processes in synthesizing diamonds using this catalyst were studied by means of optical microscope, X-ray diffractometer, SEM and TEM. The change of temperature and pressure during the diamond synthesis was analysed In the systems of powder catalyst and flaky catalyst. The Physical and chemical characteristics of MNRSPC were investigated. The results show that, first, this powder catalyst has high surface energy, high nonequilibrium carbon content, lower melting point than that of domestic NiMnCo flaky catalyst ; second, this powder catalyst has single face-centered cubic structure with lattice constant being 3.559A. The process parameters of the synthesis of MNRSPC on domestic cubic high pressure apparatus were studied for the first time. Using the optimum seeking method, the better process parameters for one-step, two-steps increasing pressure processes were determined, and the synthesis of diamond in the (?) 23 synthesis cavity