An efficient approach for computer aided-analysis and modelling of power electronic circuits is presented in this paper. It's used linearized switch characteristic and nonideal equivalent circuit model for each semiconductor device to avoid the drawbacks of ideal switch concept. To obtain a more accurate switch model far simulation, not only we use the linearization of characteristic of snitching devices, but also we take into account their dynamic properties. The switch model consists of a current source in parallel with a resistor-inductor-voltage source series network. Since the modelling resistance and inductance in the equivalent circuit are constant, the system matrix is constant, regardless of the state of switch. The linearized switch characteristic is obtained by arranging the value of current source in the model, during the simulation. No switching relationship between the externally and internally controlled switches is assumed, No prior knowledge of circuit operating is necessary in order to conduct the simulation, The network equations are generated by using modified nodal formulation, and thus, a reduction elf circuit formulation and computing time is obtained. An example is included. The results confirmed the accuracy and generality of the method.