To reveal the effects of wind power injection to voltage stability and losses of the power system, as well as the role of reactive power compensation, the bifurcation analysis method is used in this paper. Several indexes that characterize the impacts of wind power injection to voltage stability and losses of the power system are proposed for the first time (active power loss per unit etaP, reactive power loss per unit etaQ, and voltage offset per units DeltaV/P). Research result shows that reactive power compensation can delay or suppress the occurrence of saddle-node bifurcation, but it can not completely make up for negative roles of continually increasing of wind power injection; through quantitative analysis of roles reactive power compensation to reducing of losses and improving of voltage stability, the effectiveness of the proposed indexes were proved. Thus, it is a great breakthrough compared with the qualitative analysis by quantifying the results of the study.