The spore number and lesion area of maize gray leaf spot disease caused by Cercospora zeae-maydisTehon & Daniels in different layers and parts of the leaf were studied by using spray inoculation method under the field condition in Kunming,and the relationship between disease severity and the days after inoculation, time-duration of temperature and relative humidity was analyzed.The result indicated that the correlation between lesion development and time-duration of temperature 20-30 ℃,effective accumulated temperature≥10 ℃, days after inoculation, time of relative humidity≥90% and variety resistance was very significant(P＜0.01). Small lesion and few spores appeared on resistant varieties,but big lesion and more spores on the susceptible ones. Lesion occurred largely on the ear leaf and below,in the middle and front of the leaf. The lesion development was mainly longitudinal and altitudinal development was not evident.