The invention provides a modeling method and calculating method for an electromagnetic characteristic of an electromagnetic mechanism of a load switch. The modeling method comprises the steps of firstly, preliminarily selecting a plurality of key interpolation nodes according to a suction curve characteristic and determining a form of a self-defining function of reflecting the relationship between an output characteristic and a process variable of the electromagnetic mechanism of the load switch on the basis of an interpolation thought; and then determining an unknown coefficient in the built self-defining function through a latin hypercube sampling method, a finite element method and an optimization algorithm and building an approximate model for the electromagnetic characteristic of the electromagnetic mechanism of the load switch. According to the calculating method, the electromagnetic output characteristic of any process variable node of the electromagnetic mechanism is calculated according to the built model when a design parameter of the electromagnetic mechanism of the load switch changes within a tolerance range.