Abstract: The variety screening experiment for mechanical grain harvest was carried out in Zhongjing, Sichuan Province from 2017 to 2019 to screen suitable Sichuan summer maize varieties for mechanical grain harvesting and identify the factors influencing the quality of mechanically harvested grain. Factors such as mechanical grain quality, grain moisture content, and yield were analyzed based on 98 tests of 28 maize varieties. Results showed that high broken grain and ear loss rates were the main issues with the mechanical grain harvest of Sichuan summer maize. The average broken grain rate, impurity rate, ear loss rate, and total grain loss were 5.63%, 2.39%, 4.12%, and 4.76%, respectively; with ear loss accounting for 86.55% of total grain loss. Grain moisture content was positively correlated with broken grain, impurity, and grain loss rates, while there was no significant correlation between grain moisture content and ear and total grain loss rates. High grain moisture content was the main cause of grain breakage rates during harvest; delaying the harvest period could effectively reduce the grain moisture content and thus, reduce grain breakage rates. At the same time, the mismatch between the spacing of planting and harvesting rows was the main cause behind high ear loss rate (86.55% of total grain loss). Ensuring that the harvest was performed in opposite rows could significantly reduce the ear loss rate and greatly reduce total grain loss. Four maize varieties ('zhongyu 3, ' 'yudan 30, ' 'zhenghong 6, ' and 'yanke 288') were screened out, which were suitable for the mechanical grain harvest of Sichuan using the average yield and grain moisture content during the harvest period as indicators.