In view of the demand of circuit fault simulation analysis, a novel circuit simulator for fault simulation was designed to overcome the shortcomings of traditional circuit simulation tools in fault simulation. The principles and method of this simulator were proposed, which focus on the realization of the basic functions and weakens detail characteristics. Based on the method, the components simulation models and fault models with the combination of the numerical variable with logical variable were built. Moreover, the implementation algorithm and simulation flow were introduced to show how to simulate a circuit based on this simulation model. At last, an example was simulated to verify the feasibility of this method. It is shown that, this circuit simulator will become a valuable tool for the circuit fault simulation and analysis.