Abstract: Mining fractures coalesces with shallow buried cemented soft seam,which causes water and sand mixture burst into underground mine. It has a serious impact on the safety of mine production and related engineering facili- ties,so it is instructive to study the mechanism of water and sand burst caused by mining fractures in shallow buried cemented soft seam for understanding the essence of the disaster. Firstly,the limit equilibrium conditions of water and sand burst in fractures are analyzed through the mechanics model of sand body inrush in fractures. Secondly,by using the test system for water and sand burst,flow sensors and pore water pressure sensors,the simulation experiments of water and sand burst in fractures under different initial water pressures are carried out. The variation characteristics of flow rate,pore water pressure and other parameters are obtained,quantitative analysis is made on the characteristics of water and sand migration and correlation changes of physical parameters in different stages of water and sand burs. The test results show that the whole process of water and sand burst in fractures can be divided into 4 stages,namely,start- up stage,continuous outburst stage,silt blockage stage and outburst equilibrium stage. In the first stage,the flow rate increases instantaneously and the pore water pressure decreases instantaneously. In the second stage,water and sand gradually fill the channel,and the pore water pressure and water flow rate are basically stable. In the third stage,the sand body in the channel is partially silted,resulting in a gradual decrease in flow rate and an increase in pore water pressure. In the fourth stage,it can be divided into two situations: first,when the water pressure is lower than the limit water pressure,the water and sand burst stops;second,when the water pressure is higher than the limit water pressure, the water and sand continuous outburst and remains consistent. Within a certain range of initial pressure,sand body migration in a certain spatial range and the data change of pore water pressure far from the channel is lagging behind. With the increase of initial pressure,the time required for siltation and blockage decreases,which leads to the decrease of the duration of sand outburst. When the initial water pressure reaches a certain value,the volume ratio of water and sand outburst in the fracture reaches its peak value and the water pressure stability. After the test,with the increase of initial water pressure,the spatial distribution range of “collapse pit” in the middle of test chamber tends to increase.