The invention relates to a 0+ error immune electromagnetic transient simulation algorithm used under the sudden change of input quantity and belongs to the technical field of electromagnetic transient analysis of an electric system. According to the method, by means of the impulse response invariable principle, numerical sampling of a continuous signal of the system corresponds to Z conversion of a discrete signal, and the fundamental form of an element based on operation conductance and a history current item is given. Based on the form, a system network equation is obtained according to the node analysis method, and a system electromagnetic transient simulation result is obtained according to the same steps. The method has the advantages that the truncation error is smaller than that generated through currently adopted methods and the 0+ error purpose is realized under the sudden change of the immune input quantity, achieves non-linear load modeling of the electric system, solves the problem of oscillation of an electronic power switch model state variable outburst value, and provides a new way for electromagnetic transient branch-level modeling of the electric system.