Abstract: In this study, the optimal application timing of 11 representative fungicides for the control of potato late blight was investigated. The preventive effects of 5 fungicides applied at different time within 10 days before the inoculation(dbi) and the curative effects of 7 fungicides applied at different time within 24 hours post the inoculation(hpi) of Phytophthora infestans on potato leaves were tested by means of artificial inoculation. The result showed that, under the premise of achieving good control effect, the appropriate application period for fungicides protectively applied before the inoculation is much longer than that curatively applied post the inoculation. The optimal application period for 5 fungicides applied before the inoculation, with 100% control efficacy, was 3 to 10 days under tested concentration; whereas that of 7 fungicides applied post the inoculation, with the same control efficacy, was only 6 to 12 hours, which is difficult to operate in actual potato production. The results of this study indicated that, in the chemical control of potato late blight in farming practice, spray should be conducted preventively before the infection of the pathogen, and curative application of fungicides should be avoided as much as possible.