Abstract: To determine the suitable sowing date of spring maize and arrange spring production reasonably, the agricultural meteorological observation data and the meteorological data of main maize producing areas in Inner Mongolia from 1961 to 2016 are used in this study. The mathematical statistics is applied to analyze the change laws of ground temperature and frost in the 56 years. The beginning dates when the 10 cm soil temperature is stably above 8℃, 9℃, 10℃, 11℃ and 12℃ are taken as spring maize sowing indexes. By calculating the probability threshold of frost after seedling under different critical temperature conditions, the suitable sowing index and sowing dates of maize are determined. The results showed that during the 56 years, the beginning date of 10 cm soil temperature stably above 8℃ was 2-20 days ahead, the ending date of frost was 3-20 days ahead in the most regions of Inner Mongolia. It was suitable to use the beginning date whose 10 cm soil temperature was stably above 8℃ as spring maize sowing indexes in Zhalantun City, Tuquan County, Songshan District and Jungar Banner. The beginning date above 9℃ was suitable for Horqin District, the beginning date above 11℃ was suitable for Tumed Left Banner and Linhe District, and the beginning date above 12℃ was suitable for Liangcheng County. The suitable sowing date was from April 6th to May 3rd for most areas in Inner Mongolia, it was held 8-22 days ahead of the actual sowing date. So the varieties with slightly longer growth stage could be chosen.