In order to explore the impact of microplastics on soil water retention, 1 mm and 25 μm polyethylene microplastics (PE-MPs) were selected. After the soil culture, the soil moisture characteristic curves under different treatments were measured by the high-speed centrifuge method, and the Gardner model was used for fitting analysis. The results showed that: (1) A small amount of PE-MPs (0~5.00 g/kg) accumulated in the soil could enhance the soil water holding capacity, but when the cumulative amount exceeded a certain threshold (5.00~50.00 g/kg), it would lead to a significant reduction in soil water holding capacity. (2) The large accumulation of 1 mm PE-MPs had a more significant reduction effect on soil water holding capacity; a small amount of 25 μm PE-MPs had a more significant increase effect on soil water holding capacity. (3) After invading into soil, the 1mm PE-MPs mainly affected the macropores and effective pores, and had a greater impact on the effective soil moisture content; while 25 μm PE-MPs mainly affected the micro pores and had a greater impact on the wilting coefficient. This study can provide a theoretical basis for water migration simulation and agricultural ecological risk assessment in areas with high agricultural film residues.