Abstract: Accurate source location is the basis of most micro seismic studies. Because of large location error, the relationship between station density and location error is analyzed. A 3-D monitoring system model is established, and the target equation is set up by using the time difference. The influences of location method, velocity error and source position on source location are studied by using the PSO algorithm. It is found that the wave velocity error has a great influence on the location error, and the error caused by low velocity is higher. The location in station envelope is better than that in the external. The higher the velocity error, the more obvious the effect. The station density has a significant effect on the source location which is mainly reflected in two aspects: the first is the number of station plane, the location accuracy from high to low followed by the arrays of multiple plane, single plane near source, single plane far from source; the other is the number of sensors, and the number of the whole monitoring system has a close relationship with the station number. It is shown that there is a negative exponential relationship between the location error and the station number. The results of this study can provide some reference for the researches on mine seismic monitoring and local scale earthquakes.