Abstract: In order to measure the acoustic source level of the depth-detonating explosion source accurately, three limiting conditions for obtaining ideal explosion signal are given according to the process of underwater explosion. Then, the value range of horizontal distance and hydrophone depth for measuring three explosion sources (B300, B100 and B50) are obtained. According to this range, the B300 explosion source is tested at sea, and the ideal explosion signal is obtained. Meanwhile, the energy distributions of the sound signal in different time durations are calculated, the errors caused by approximate calculation of two different signal interceptions are 0.64 dB and 0.53 dB respectively. The experimental results show that the limiting conditions given in this paper can be used to guide the design of the explosion sound source level measurement scheme in sea trial, so that a more accurate explosion sound source level can be obtained.