Abstract: This paper discusses the influence of noise from an electric generator on torpedo self noise with regard to high noise of thermal power torpedo. The output noise of built-in power source is generated from the electric generator, and verified by spectrum analysis and analogue test. The noise enters the receiver from the converting circuit of homing receiver and transmitter through cables, ground wire and the homing transmitter. The characteristic of the noise and its influence mechanism on homing range are analyzed. The countermeasures to improve circuit design for receiving and transmitting isolation are proposed to enhance the ability of blocking noise and filtering power source. The test results show that the countermeasures can restrain the noise by 10dB to 20dB to increase the homing range to a new level, and reduce the probability of false alarm in passive homing to improve the performance of homing system and to increase the reliability of homing system operation.