The paper uses the “equipment level→link level→process level” three-level evaluation method to evaluate the probability and frequency of industrial process interruption caused by voltage sag. According to the equipment voltage tolerance curve and its uncertain region, the equipment voltage sag fault probability evaluation model is established. In order to reduce the evaluation error, a voltage sag normalization method is proposed. According to the process immunity time of each physical parameter of the link and the minimum restart time of the corresponding equipment, accurately quantify the redundancy of each physical parameter of the link, and correct the failure probability of the corresponding device, and determine the link according to the function of the device and the connection mode between the devices. Structure and calculate the probability of interruption. By introducing the calculation method of the weight coefficient in the analytic hierarchy process, the weight coefficient of each link is calculated, and the probability of the industrial process voltage sag is calculated by combining the link interruption probability. The example analysis results verify the correctness and feasibility of the proposed model.