Objective　To investigate the effect of various fa ctors on disinfection efficacy of ultraviolet ray. Methods　The germicidal exper iment was carried out in a purified chamber. Standard bacteria sprayed in the p urified chamber was irradiated by using an 100 μw*cm-2*s-1ultrav iolet lamp under different c onditions. Results　The disinfection efficacy showed correlation with tempe rature, humidity, intensity, way of radiation, electric fan running or not and different microorganisms, among which temperature showed the strongest effect on killing rate. Under the same condition, the efficacy of ultraviolet l amp in killing staphylococcus albus is superior to that in killing escheri chia coli, and the efficacy of killing the spore of bacillus subtilis is the l owest. Conclusions　The way of air disinfection by a high intensity and low ozone ultraviolet lamp irradiation is reliable, safe, practical and feasi ble.