Abstract: With the development of social economy and the continuous increase in population, the agricultural planting structure in China has gradually simplified, and the biodiversity of the agricultural system has drastically reduced. Agricultural development faces the challenges of ensuring food security and sustainable development. In this article, we reviewed the ecological mechanism of mixed cropping of varieties of crops in ecology and agronomy researches from perspectives of complementary effect, selection effect, resistance to pathogens, mycorrhizal symbiosis, and plant-soil feedback effect; and described the potential risks, which are affected by variety, environment, and management aspects. Studies on mixed cropping of crops varieties in natural and agricultural systems have shown that biological and genetic diversity is usually beneficial to ecosystem function. Mixed cropping of varieties improves biodiversity, which is of great significance for improving crop productivity and reducing pests and diseases. We summarized the screening principles and basis of functional trait evaluation of mixed cropping of crops varieties. The selection of varieties should be based on functional traits and goal-oriented and actual production needs, and the performance of varieties should be comprehensively evaluated by yield, yield stability, and stress resistance.