Abstract: The method of stratified digging was adopted to study temporal and spatial distribution of fine roots in a four-year old poplar-winter wheat intercropping system relative to nitrogen fertilization and its difference from that in the winter wheat mono-cropping system, and to explore effect of the intercropping system reducing nutrient loss with runoff. Results show that (1) the winter wheat in the mono-cropping system was higher than that in the intercropping system in fine root length density and root dry weight per unit of soil; (2) the peaks of root length density and root dry weight per unit of soil appeared during the wheat milking stage in both systems; (3) with increasing nitrogen application rate, both the wheat and the poplar increased in fine root length density and root dry weight per unit of soil and for poplar the increase mainly occurred in the ＞40-80 cm soil layers; and (4) intercropping reduced nitrogen loss with leaching by 49.08%-55.49%.