Microplastic pollution has become a concern around the world, when microplastics interact with other pollutants such as heavy metals in the soil system, microplastics will adversely affect the growth and development of plants, but the interaction between microplastics and heavy metals on plants is less studied. In this study maize seeds were used as the research object to explore the effects of polypropylene microplastics(PP-MPs) and heavy metal cadmium (Cd) on seed germination, seedling growth and oxidative stress of maize with different particle sizes (50 μm and 100 μm). The results showed that the germination rate, germination potential and viability index of PP-MPs+Cd treated seeds were improved, Cd treatment and PP-MPs treatment had inhibitory effects on the mean germination time (MGT), and Cd, 50 μm PP-MPs+Cd and 100 μm PP-MPs+Cd treatments all had certain inhibitory effects on MGT to varying degrees. Cd and 100 μm PP-MPs+Cd treatment inhibited the growth of maize seeding roots and shoots on both the third and the seventh days. On the third day, the fresh weight and dry weight of Cd treatment and 100 μm PP-MPs+Cd treatment decreased by 8.32%, 17.31%, 9.91% and 17.86%, respectively. Overall, PP-MPs+Cd treatment promoted catalase (CAT) and peroxidase (POD) activities in maize roots and shoots, but POD activity decreased by 2.82% at 100 μm PP-MPs+Cd treatment. This study provides a basis for the toxic effects of microplastics and heavy metals on the growth of maize and other crops.