Abstract: The SCR invertor equipment is researched and its mathematic models are established in this paper. The ideal wave forms of U_f and I_f are analysed and compared with the wave forms in actual test. The choice of SCR capacity is discussed. The problems concerning the stable shutting of SCR are put forth. The relation among the reverse voltage, holding time and out-put power is discussed and the difference in working point stability for different out-put characteristic curves is also studied.