Abstract: Power grid of China has complex characteristics and many operation constraints. With the construction of the electricity spot market, higher requirements are put forward for the accuracy of security check calculation. Therefore, the content of security check and the factor which affects its accuracy are analyzed, and a refined security check scheme in the provincial power grid for electricity market operation is proposed. The scheme includes the following three aspects. As for the power grid model, the gridconnection of low-voltage power plant and the equivalent calculation method of the tie line is proposed, and the re-commissioning operation of shutdown equipment and the future operation condition calculation of equipment are analyzed and designed. In terms of algorithmic flow, the relationship between spot market optimization clearing and security check is sorted out, and the mixed iterative calculation process of market clearance, cross-section quota calculation and security check is proposed. In terms of auxiliary information,the reservation calculation method of each regional cross-section as well as the whole network is proposed for regional transmission cross-sections based on the relationship between equipment and cross-section or between the cross-sections.Finally, it is proven that the proposed scheme can effectively improve the accuracy of security check through the actual operation of a provincial power grid in China.