Considering the actual situation of mines, the microseismic event probability factor, the monitoring area importance factor and the network layout feasibility factor were introduced to rebuild the objective function of monitoring network optimization based on the theory of D-optimal design. Taking microseismic monitoring in a phosphate ore for example, the mining area was zoned according to the importance of the monitoring area, the feasibility of the network layout, etc., and then the reference values of relevant factors were given by the expert investigation weight method. The monitoring region was rezoned according to the differences of these influence factors, and the integral form of the objective function was given with the control point coordinates of the monitoring region as the corresponding range of integration. The dynamic optimization design principles of microseismic monitoring were proposed, and the optimal plan of a microseismic monitoring network in this phosphate ore was established finally based on the above study. Field blasting test shows that the monitoring network is rational and valid to a certain degree, the average error of the three coordinate directions is 6.74 m, the maximum error is 10.05 m, and the spatial positioning error is 12.51 m. This positioning accuracy can satisfy the field engineering demand.