Shehong, Renshou and Guangan, the 3 typical hill counties in Sichuan Province, were selected in this study. The yield of combination of maize-soybean from 2004 to 2012 in these sites was investigated, and the compositions for the total yield in the maize-soybean inter-cropping system, which was dominant in Southwest China. Based on this, the largest theoretical yield of the intercropping system was evaluated and the relationship between yield and the compositions were discussed. The results demonstrated that, the low yield of combination of maize-soybean was accounted for up to 80.2% of the total areas in Sichuan Province. In addition, the largest theoretical yield in this system was significantly higher than the actual yield, which suggested that there were great potential for improving yield in maize-soybean intercropping system in Southwest China. Furthermore, the path analysis indicated that different yield components had their distinct contributions for the total yield, and among them the effective stalks of maize and soybean were the most important determinants. On the other hand, the soil fertility components including organic matter, total nitrogen, available nitrogen, available potassium could also make great contribution to the total yield of maize-soybean intercropping system. Therefore, the proposals for the high-yield cultivation for maize-soybean intercropping system should be employed strictly; the effective stalks of maize and soybean should be increased; and effectively soil improvement and rationalized system were employed. In a word, the high yield of the maize and soybean could be achieved through employing these effective strategies described above.