Abstract: Based on the employment of 0 cm soil temperature ≤0℃ as climatic index for frost,the data of first frost dates collected from 14 meteorological stations in Chifeng City were analyzed by basic statistical methods and climate diagnosis methods.The result showed that the average first frost date is September 21st and the spatial distribution difference of the first frost dates was obvious.The average first frost date in recent 50 years obviously delayed at a rate of 1.5 d/10a.Mutation of the first frost date was observed in 1997.The average first frost date after 1997 was 4 days later than that before the mutation.