A field plot experiment was conducted to explore the effects of cross ridge covered with plastic film on soil net nitrogen mineralization in Wulongchi small watershed during maize growing period. Results showed that the soil net nitrogen mineralization contents under cross ridge covered with plastic film were significantly lower than those of non-mulched treatment at the mid-term stage of seedling and the early stage of jointing, and the decreases were 7.8%～57.0% and 2.2%～52.8%, respectively. While at the later stage of jointing, heading stage and maturity stage,, the former were significantly greater than the latter and the increases were 352.9%～703.3%, 52.5%～311.0% and 15.2%～334.8%, respectively. The higher correlations existed between the soil net nitrogen mineralization contents under cross ridge covered with plastic film and the soil moisture, temperature and total nitrogen contents at the seedling stage, jointing stage, heading stage and maturity stage (0.6＜Grey correlation degree≤0.8). The soil net nitrogen mineralization contents under cross ridge covered with plastic film showed a significant linear relationship, with soil temperature at the seedling stage (F=7.205, P=0.023), with soil moisture and temperature at the jointing stage (F=36.861, P=0.001), and with soil moisture at the maturity stage (F=42.438, P=0.007).