Abstract: On the basis of theoretical analysis, a mechanism of soil temperature changing under soil cover and the influence of spectral transmission of mulch materials on soil temperature were given. Through experiment, the spectral transmissions of mulch materials used in plant cultivation, such as transparent LD PE film, black LD PE film and black paper, were determined in the wave length from 300 to 800 nm respectively. The quantitative effects of soil cover with these mulch materials on the soil temperature were studied by means of field test.