Abstract: To clarify the relationship between the initial occurrence of grape downy mildew and sporangia, meteorological factors and grape varieties, the initial occurrence periods of grape downy mildew of Ruby Seedless, Muscat Hamburg and Cabernet Girnischt were investigated for 6 consecutive years. A spore trap device was installed to collect the grape downy mildew spores in the air. The meteorological data of field were detected by a small climate station. The relationships between temperature, humidity, rainfall and the initial occurrence of grape downy mildew were analyzed. The results showed that downy mildew spots were seen in field after 10 days of the discovery of grape downy mildew spores. The downy mildew occurrence period of different grape varieties was different, that of Ruby Seedless was the earliest, followed by that of Muscat Hamburg fragrance, and then was that of Cabernet Girnischt. The incidence of grape downy mildew was closely related to temperature, humidity and rainfall, in which the rainfall was the main factor. Based on the above data analysis, this study proposes a direct and simple method for the prediction of grape downy mildew, which could be a basis for the prevention and control of this disease.