Abstract: Abstract: It is clear that the effect of voltage sag on the performance of sensitive equipment is a very concerned problem for manufacturers and users, and it is also the precondition of choosing a method to mitigate the influence of voltage sag on sensitive equipment. This paper proposes a method of using process immunity time curve to study the influence of voltage sag characteristics on sensitive devices, and ASD structure is briefly introduced, and the correctness and feasibility of MATLAB / Simulink are verified by modeling, simulation and analysis.