Abstract: Based on the results gotten from model experiment with similar material, the main features ofcoal mine surface moving under thick water-bearing alluvium condition are analysed comprehensively and calculated with limit element method; the strata liquidation under thick water-bearing alluvium condition is studied with mathematics and rnechanics; the moving mechanism of continuous de formation, appeared under dynamic load, of saturated sand-soil strata in alluvium is explained; and significant conclutions are came to.