In order to scientifically and reasonably evaluate the power grid operation safety capability， this paper first adopts a comprehensive weighting method of the rank-related subjective weighting method and the index information amount to integrate objective weights for comprehensively determining the final weight of the grid operation safety capability evaluation index system. Then， an improved gray correlation comprehensive evaluation model with resolution coefficient is constructed. Finally， the safety capability of a power grid operation in six periods is evaluated， and compared with the traditional gray absolute correlation model. Results verify the validity and practicability of the proposed model.