The study was conducted to determine the plastic film mulching on the soil physical,chemical and biological properties such as soil microbial population,enzymatic activity,microbial biomass carbon and active microbial biomass at the 0-20 cm and 20-40 cm soil layers under the poplar field conditions.The recults showed that the soil water and alkaline hydrolysis N contents within the depth of 20 cm increased obviously with the plastic film mulching compared with the traditional treatment while the pH value and the contents of organic matter,total nitrogen and available P decreased;the numbers of bacteria and fungi increased by 44.89%and 42.58%,respectively;the number of actinomyces had no significant changes;the activity of urease enzyme deceased by 13.02%;the activity of catalase enzyme, invertase enzyme and polyphonic oxidace enzyme improved by 29.25%,83.66%and 28.95%,respectively,which was in favour of decomposition and utilization of the soil nutrients.The changes between that in the 0-20 cm and 20-40 cm soil layers were similar while the variations between the traditional treatment and plastic film mulching were less in the 20-40 cm soil layer,which indicated that the effects of plastic film mulching on poplar field weakened with the increase of soil depth.It is concluded that plastic film mulching obviously ameliorated the ecological environment of the soil in the poplar field,especially in the topsoil.