Abstract: For the study of detecting sonar signals with complex time-frequency composition under noise-background by human auditory system, the problem of auditory response to transitions between signal frequencies has been examined through a number of tests. According to the results of measurement within a frequency .region of 850-1130 Hz, an equation (τ△F=1-2) to define the ambiguity region of responding to frequency transitions by human auditory system is found, where △F and τ are the difference and duration of the transition between two frequencies respectiyely. when τ△≤1, the human auditory system hardly can sense transitions between frequencies, however very clearly sense when τ△F≥2.