A novel four-step commutation is proposed with unequal step for each bidirectional switch cell on the basis on analysis of many proposed commutation methods of matrix converter in this paper. The first and fourth step can be shorter than the second or third one because the actual switching on or off of output current happens on the second and third steps. Here the second step is equal to the third one. This method is implemented with four steps by programming in VHDL language. First, the special flip-flop, 74AHC16373, is obtained by programming so as to make input sector signals, output sector ones and active switching time PWM ones synchronize. Second, the required switching states are flexibly realized in the form of the look-up table by programming in VHDL language for 36 switching combinations of input sectors with output ones. Third, the obtained switching states are judged whether they need commutation by delayers. Finally, the novel method proposed is implemented by switching sequencers. The simulation results have verified its feasibility.