To address the decline in maize grain quality caused by increased planting density in oasis irrigation areas, this study examines the effects of intercropping pea on maize grain quality under different planting densities, aiming to provide theoretical and practical guidance for optimizing high-yield, high-quality maize cultivation systems. A split-plot experiment was conducted from 2020 to 2021, with monocropped maize (M) and intercropped maize with pea (M||P) as the main plots, and different maize planting densities as subplots: for monocropping, 78,000 plants per hectare (M1, low density), 103,500 plants per hectare (M2, medium density), and 129,000 plants per hectare (M3, high density); for intercropping, 45,000 plants per hectare (M1||P, low density), 60,000 plants per hectare (M2||P, medium density), and 75,000 plants per hectare (M3||P, high density). The results showed that increasing planting density significantly improved maize grain yield and biological yield, while intercropping with pea further enhanced these effects. Among the intercropping treatments, medium-density maize (M2||P) achieved the highest grain and biological yields, increasing by 34.6%–36.6% and 30.0%–39.3%, respectively, compared to low-density monocropped maize. As planting density increased, starch content in maize grains significantly increased, whereas protein and fat contents significantly decreased, with the total yield of nutritional components first increasing and then declining. Intercropping with pea significantly improved maize grain nutritional content and total nutritional yield, enhanced the positive effect of higher planting density on grain starch content and total nutritional yield, mitigated the negative impact of increased density on protein content, and reduced the decline in total nutritional yield observed at high density compared to medium density. Higher planting density significantly reduced the content of phenylalanine, leucine, isoleucine, and valine in maize grains while significantly increasing tryptophan and lysine concentrations; intercropping significantly increased phenylalanine, leucine, isoleucine, and valine levels and alleviated the reduction in phenylalanine and leucine content caused by increased planting density, with the best effects observed under medium-density intercropping (M2||P). Overall, both increased planting density and intercropping significantly improved the comprehensive performance of maize, with the best overall performance achieved by intercropping pea and a maize planting density of 60,000 plants per hectare (M2||P), yielding a performance score of 0.47. This planting model maximizes grain yield while enhancing grain quality, making it a feasible and effective cultivation strategy for improving maize production in the Hexi Oasis irrigation area.