Optoelectronic characteristies of the SiCl-ZGeZ/SiC heterojunction photodiode are simulated using MEDICI after the theoretical investigation of key properties for SiCl-xGex. The calculations show that SiCl-xGex/SiC with x=0.3 may have a small lattice mismatch with 3C-SiC and a good response to the visible light and the near infrared light. The response spectrum of the SiCl-xGex/SiC heterojunction photodiode, which consists of a p-type SiCl-xGex absorption layer with a doping concentration of 1×1015cm-3 ,a thickness of 1.6μm and x=0.3, has a peak of 250mA/W at 0.52μm and the peak can even reach 102mA/W at 0.7μm.