Different planting densities and mixed-cropping methods were studied to see how they affect maize growth and yield. Higher planting density led to increased grain yield, dry matter accumulation, and leaf area, but decreased chlorophyll content and photosynthetic rate. Mixed-cropping at high density increased leaf area, chlorophyll content, photosynthetic rate, and dry matter accumulation compared to monoculture. Mixed-cropping also improved the distribution of nutrients to the grain, resulting in higher grain yield. This study shows that mixed-cropping can significantly increase maize yield in densely planted fields.