With the rapid development of Smart Substation in China, the secondary safety measures of Smart Substation have also received more attention. In the process of operation and maintenance of smart substation, it is necessary to isolate secondary equipment safely and reliably in order to avoid affecting the safe and stable operation of power grid. Therefore, this paper puts forward the concept of secondary equipment state, and models the transfer of secondary equipment between normal state and abnormal state in a mathematical way. On this basis, a mathematical reasoning method for checking the operation of Ancuo based on logical calculation is proposed. The correctness of this mathematical reasoning method is verified by two examples, Yongdeng Change and Mozhugong Card Change.