Abstract: This experiment was conducted in a loamy brown earth derived from loesslike parent material at Shenyang Agricultural University during 1987 ~ 1994. The main results showed that the average contents of alkali-hydrolyzable-N (1mol NaOH-N) and aminoacid-N in all covered treatments declined 6.46mgkg-1 and 21.6mgkg-1, compared with uncovered treatments. However, no significant effect was found on total N, NO3--N tended to be accumulated in the top layers of the plots covered with the plastic film, because of much water with soluble NO3- moving toward these top horizons. Soil biomass-N increased greatly by covering practice, which could lead to the improvement for soil nitrogen supplying ability. In addition, the application of organic manure could improve the levels of total N, alkali-hydrolyzable-N, NO3--N and organic components of nitrogen in soil. Therefore, more manure should be applied to soil covered with plastic film so as to improve covered soil fertility.