Abstract: Traditional interaction security measurement method can not reflect the inherent security of software interaction basic attributes. In order to remedy this deficiency, this paper presents a method for the metrics of interaction inherent security. Through analyzing intrinsic security problems existed in the basic attributes of interaction, we puts forward the concepts of input-point complexity and input-point concentration ratio etc.,proposes a metric model of the inherent security of interaction of software based on input-point concentration ratio,and measures the inherent security of interaction of software through three examples. The measurement results show that it is effective by using input-point concentration ratio to measure inherent security of interaction. This method greatly reduces the disturbance of the changing of external factors on the metric results and, therefore,improves the credibility, integrity, and generality of the results.