Abstract: In order to tackle the top coal reserving problem of large span open-off cut at fully mechanized caving face with soft-weak and thick coal seam in Sangshuping Coal Mine, FLAC^3D was used to simulate the distribution of plastic zone in different spans, and then the stepped open-off cut was proposed. The results showed that: compared to the distribution of along bottom and reserving top coal, the stepped open-off cut's plastic zone has no significant change, and the distribution of tensile yield in roof and floor was same too. The top coal of side slope extension was the main area of tensile yield, while the secondary buttock's distribution of tensile yield enlarged remarkably. The stepped open-off cut can effectively reduce the difficulty of reserving top coal in large span open-off cut under the soft-weak and thick coal seam. Another, it avoids the problem of triangle coal in the coal floor, and improves the mining rate of coal and the speed of coal face advancing.