Abstract: Based on the conditions of working face 3105 in Sangshuping coal mine, by using sonic wave test and numerical simulation, a study for the floor failure law of mining coal in retained gateway along goaf was done. Sonic wave test results indicated that the damage depth of the coal seam floor was about 13.2~14.6 m, and numerical simulation showed that the damage depth was 13.0~14.5 m, the results obtained by both methods were in good agreement. Comparison of the damage depth of the coal seam floor and the normal conditions indicated the technique of retained gateway along goaf will not result in significant influence on the damage depth of seam floor. The results provides the foundation for determination of the law of disturbance and damage of seam floor during mining in working face under pressure by using teh mining technique of retained gateway along goaf in China.