GUI program's idle state usually causes low efficiency of fuzzing test.This paper tries to solve idle state detecting problem based on function trace by nature language processing method.It first analyzes the difficulties that traditional program analysis method faces in idle state detection,and then proposes an idle state detecting method based on Bi-Gram module and statistical analysis.Bi-Gram algorithm transforms the function trace of the GUI program to probabilistic characteristics sequence,then segregates the idle state probabilistic characteristics sequence from prgram's probabilistic characteristics by variance characteristics in idle state probabilistic characteristics sequence.The algoritnm finally extracts idle state features which applied to the real-time idle state detecting algorithm.Experiments of source code and binary program show that the new method is more efficient and accurate than traditional method.