Abstract: It is an important way for preventing “white pollution” to develop and promote environment-friendly biodegradable plastic film, which is holding back the development of agriculture. Compared with ordinary plastic film, biodegradable plastic film takes less time to degrade, and has low molecular weight residues, mainly linear low density polyethylene (LLDPE). The research into the effect of low molecular weight polyethylene (LMWPE) on crop growth and soil microenvironment was of great significance to promote use of biodegradable plastic film. In the experiment, we simulated natural conditions and LMWPE were added in different dosages to pot-soils in which horse bean (Vicia faba Linn.) were planted. Dosages of LMWPE were 0.028 g·kg^-1, 0.28 g·kg^-1, 1.40 g·kg^-1, 2.80 g·kg^-1, which were decided according to residue amounts in soils with 1, 10, 50, and 100 years continuous plastic film mulching. The plant height, leaves number and pod number, as well as the activities of urease, peroxidase and sucrase in soil were measured during whole growth period of horse bean. During horse bean growth period, plant height, leaf number and activities of urease, peroxidase of soil under LMWPE treatments were increased compared with those under CK₁ (cultivation of horse bean without LMWPE). The more LMWPE were added, the more significant the effects were. But soil invertase activities and horse bean pod number were not significantly affected by LMWPE. Formation and growth of horse bean roots impacted activities of three soil enzymes significantly. Soil enzyme activities were significantly correlated with plant height, leaf number of horse bean, but not with pod number. It showed that added LMWPE in soil had activating effects on horse bean growth and soil enzymes activities. 2.80 g·kg^-1 LMWPE showed most obviously effects.