Three kinds of CMOS compatible photosensors, P+/N_well photodetector, N_well/P_sub photodetector and N+/Psub photodetector, were designed by using SMIC 0.18μm standard CMOS technology. Some critical parameters, such as responsivity, dark current and maximal response wavelength were analyzed based on the mathematic model established. The influences of some technology parameters, such as doping concentration, junction depth, were pointed out as well. The experiment results indicate that P+/N_well photodetector can reach a maximal sensitivity of 0.08 A/W at 460nm with 55nA/cm² dark current, N_well/P_sub photodetector has a maximal sensitivity of 0.35A/W at 580nm with 64nA/cm² dark current and N+/P_sub photodetector attains a maximal sensitivity of 0.29 A/W at 580nm with 600nA/cm2 dark current. The test results show that the photodetectors designed agree with theoretical analysis basically and have prominent performance on sensitivity and response wavelength.