The structures of a family of pure ZnS and ZnS eloped by activator Cu and Mn with different concentration ranges under sintering temperature ranging from 600℃ to 1200℃ have been investigated by x-ray powder diffraction method. Using the absolute standard method, the weight ratio of a phase to 3 phase of ZnS microcrystal and the constant Kβα of this method have been determined. The results show that the transition temperature of low temperature βphase to high temperature α phase is 1020℃ for pure ZnS, as generally accepted. When the concentration of doped Cu is in excess of 1×10-3, the phase trasition temperature (PTT) moves obviously to high temperature. As the concentration of Cu reaches 2×10-3, the PTT is higher than 1200℃. The results can be explained by postulating when the concentration of Cu is greater than the solubility of Cu in ZnS, a separate phase of copper sulfide serves as a nucleating phase for the growth of cubic ZnS and thus promotes the hexagonal-to-cubic transition. When the concentration of doped Mn is in excess of 1×10-3, the PTT moves obviously to low temperature. As the concentration of Mn reaches 5×13-3, the PTT is lowered to 730℃. In the range from 700℃ to 950℃, the weights of α phase and βphase are close to each other. The PTT of ZnS: Cu 2×10-3. Mn 5×10-3 are also determined approximately as 1100℃.