Distributed generation connected to grid will have certain impact on voltage stability of power system. At first, the comprehensive dynamic equivalence circuit of internal grid of DG integrating bus is implemented; and on the basis, the method of dynamic equivalent circuit is further extended to the grid-connected DG which is regarded as a “negative” load; and general impedance modulus margin index is put forward to evaluate the system static voltage stability. The impacts of the output and their different installation methods of DG on system voltage stability and optimization of reactive power compensation are researched based on general impedance modulus margin index. At the last, the proposed method is proved to be a practical and convenient method that is suitable to study the static voltage stability of grid-connected DG. This work is supported by National Natural Science Foundation of China (No. 51577053).