Abstract: The study of mechanical grain harvesting quality and its influential factors is significant for popularizing mechanical maize harvesting technology in Shanxi Province and enhancing the core competitiveness of the maize industry. To study the influence of harvest time on the quality and yield of maize mechanically grain harvested, five maize varieties suitable for mechanical harvest were harvested at six times (Septmber 24th, and October 1st, 8th, 15th, 22th and 29th) by the same harvester and driver. The grain moisture content, broken rate, impurity rate, as well as ear loss rate, grain loss rate, total loss rate and yield of maize were investigated. The results were as follows: first, the grain moisture content declined gradually with a delayed harvest time. With a delayed harvest time, the grain broken rate and loss rate decreased rapidly in the early period but was stable and slightly increased in the later period. Furthermore, with a delayed harvest time, the impurity rate declined gradually and tended to be stable at the end. Finally, with a delayed harvest time, the ear loss rate increased gradually. The average yield when the field was harvested on October 15th was 11.9% higher than that harvested on September 24th. The high grain broken is the main factor limiting the quality of mechanical grain harvesting of spring maize in Shanxi Province. The relationship between grain moisture content and broken rate could be fitted in the model y=0.03x²−1.224x+16.78 (R²=0.802^**). The grain broken rate was the lowest when its moisture content was 20.4%. When the grain moisture content was between 15.6% and 25.2%, its broken rate was less than the national standard of 5%. Choosing the optimal variety for mechanical harvest in the spring maize area of Shanxi Province and harvesting on October 15th could guarantee harvesting quality and yield. ‘Changdan 511’ ‘Dika 159’ and ‘Changdan 716’, which have both perfect mechanical harvest quality and high yield, could be used as mechanical harvest varieties in the spring maize area of Shanxi Province.