According to short-circuit current calculation principle based on variable structure model, zero impedance branch is used to simulate the circuit breaker. The short-circuit current of circuit breaker can be calculated when the short-circuit fault occurs on each side of the breaker at different time with the model. The model can be useful for the selection and verification of electric equipment as well as the critical issues to the selection and parameter tuning of relay protection. The program design steps are given in the paper. Combined with one example, the calculation obtained by the program using C language is compared with the result obtained by the method of symmetrical component to check the practicality and correctness of the algorithm.