Abstract: Aimed at the "dimension explosion" in the application of Markov method in system reliability assessment, an algorithm for automatically generating system state transition probability matrix is proposed, which reduces the difficulty of manual modeling caused by "dimension explosion". To solve the problem of low efficiency caused by piecewise modeling for considering periodic test, a modeling algorithm was proposed to automatically calculate the probabilities of system states under periodic test conditions. Software development was done based on MATLAB/GUI platform, with this software, the difficulty of modeling would be reduced and the efficiency of modeling would be improved. The effectiveness and correctness of the software were verified by an application case of reactor protection system of nuclear power plant.