Taking the grain yield of 11 prefecture level cities in Hebei Province as the research object, this paper selects 14 factors which are most closely related to the grain yield, and analyzes the influence of different factors on the grain yield by using the factor detection and interaction detection analysis method of geographical detector. The spatial distribution pattern of grain yield and the main influencing factors of different kinds of grain yield in prefecture level cities were analyzed. The results showed that: the total sown area of crops, cultivated land area, agricultural mechanization level, agricultural technicians, fertilizer application amount were the significant factors affecting grain yield. The interaction among cultivated land area, crop planting area and agricultural, forestry, animal husbandry and fishery practitioners was the strongest. In the use of agricultural machinery, the use of combine has greatly affected the total grain output of Hebei Province.