The effect of planting density on maize yield and yield components were studied using 4 commercial maize hybrids and 4 crosses. It was found that, although no difference in the grain yield was found between the low density and middle density treatments when fertilizer condition was the same, increasing planting density resulted in lower kernel weight per plant, the number of kernels per ear, and 100-kernel weight, but higher barrenness rate. The yield decreased by 15.5% in high density. Correlation analysis showed that barrenness rate was the most important factor which affects maize grain yield.