Based on Matlab/Simulink platform, a method of designing the variable DC voltage power source, variable AC voltage power source and variable AC voltage and variable frequency power source block is proposed. The functions of variable voltage or variable frequency power sources are realized by combining controlled voltage source with self-defined piecewise linear function. Variable DC voltage power source and AC voltage power source are built by using the existing models in Simulink. The S-Function description, which signal parameters are arranged in the matrix, was presented in variable AC voltage and variable frequency power source block. These blocks are first encapsulated as Simulink blocks, then embedded into Matlab/Simulink platform to extend the Simulink warehouse. The simulation has demonstrated the feasibility of our method. The novel designed variable voltage or variable frequency power source block can introduce great convenience for analyzing dynamic behavior and performance of power electronic system. The designing idea has universal use to extend the warehouse of the other simulation software of circuits.