Abstract: Aiming at the problems to obtain excitation functions of J -K flip-flops by its state transition relation, and based on the analysis for intrinsic relation between state transition table with characteristic equation of J -K flip-flops,the paper gives a modified method to obtain excitation functions which can efficiently simplify the process. Using this method,even if without too much skill for logic function transformation,one can directly obtain the excitation functions from the state transition table,and the excitation functions have simplest formal.