Abstract: For discussing the prohibition effect of polyacrylamide (PAM) on grassland desertification in farming-pastoral ecotones in the north of China, through field plot compared experiment and indoor analysis, it studied the effect of different dose polyacrylamide (PAM) on soil particle composition by two factors complete randomization design. The results showed that PAM within 30～120kg/hm2 accelerated the reduction of sandy particle (2～0.02mm ) content and the increasing of clay-silt particle(<0.02mm) content , improved the coarsening of soil. The best effect was 30 kg/hm2 of PAM applying, the reduction range of sandy particle content was improved 6.95~11.29 percentages and the increasing range of clay particle was improved 6.91~12.54 percentages compared with control.