Abstract: Plastic film mulch has been widely used in agricultural production in southwest China, while there are only few studies about its effect on soil nutrients. In order to reveal the effect of plastic film mulching on soil nitrogen, a field experiment for exploring soil temperature and moisture, nitrogen and pepper yield under plastic film mulching was conducted in Beibei, Chongqing during May to September in 2014. The warming effect of plastic film mulching was obvious and increased with the depth of the soil layer, the average temperature of 10, 20 to 30 cm soil increased by 2.3, 2.8 and 2.0℃. But the impact on soil moisture was not obvious. In film mulching growing condition, the total nitrogen, available nitrogen, ammonium nitrogen and nitrate nitrogen in soil reached 1.30 g/kg, 150.83 mg/kg, 112.25 mg/kg, 105.80 mg/kg, and increased by 7.44%, 32.84%, 88.72% and 73.90%, respectively. In addition, plastic film mulching could promote plant development and increase the yield of pepper, made the flowering and fruit bearing period 4 d in advance, and the fructescence 5d ahead of schedule, and increased the yield by 14.11%. Therefore, plastic film mulching has a positive role in improving soil temperature and moisture condition, enhancing soil nitrogen content and increasing crop yield.