Abstract: During the process of sand and stone backfilling, such abnormal phenomena like instable backfilling height, large extent of the simulated casing stress, which directly affect the safety of project. By preliminary analysis, the behavior of sand and stone when backfilling is the major factor that leads to instable backfilling height and large extent of the simulated casing stress. Using simulated shaft for sand and stone deposition experiments, the results show that the fine particle is one of the prime reasons leading to instable backfilling height. and the strain of the simulated casing increased abruptly to one time greater than before in the process of the "abrupt deposition".