The invention relates to a method for modifying network state equations of circuits according to switch states. The method comprises the following steps of: (1) writing a system state equation of a circuit; (2) enabling an ideal switch in the circuit to be equivalent to a basic branch element; and (3) modifying the system state equation of the circuit. According to the method provided by the invention, the state equation of the circuit is modified according to the on and off states of the ideal switch in the circuit; and compared with the traditional circuit analysis method, the method does not need to regenerate a circuit equation and only needs to modify the branches undergoing switch state switching, so that the calculation speed of the method is considerably higher than the calculation speed of the existing circuit analysis method.