Abstract: A laboratory simulation of alternate freezing and thawing was carried out to investigate its effect on the structure of black topsoil. The results showed that: 1) Freezing and thawing action increases topsoil volume and decreases its density, and as a result, the big soil aggregates were split into smaller ones and their average weight, size and stability decreased; 2) Structural deterioration to soil was mainly affected by soil moisture and times of freeze-thaw; 3) Freezing and thawing action destroyed physical properties of the black topsoil and decreased cohesion and anti-scouribility of black soil, which is the major reason for serious freeze-thawing erosion in black soil region in spring time.