Abstract: For some mufflers with high transmission loss, the single noise source generator of existing white noise test equipment cannot meet the test requirements of the noise reduction amount. In this paper, the acoustic performance of muffler is tested by the combination of low frequency and medium frequency noise generators and the vertical connection between the transition pipe and the test pipe. In order to solve the problem of random fluctuation of the spectral characteristics of output noise signal, which is caused by the change of acoustic impedance at the junction of the transition pipeline and the combined sound source system, a correction method for combining noise signals is proposed. This method is based on the four-sensor method to measure the acoustic impedance of the transition pipeline. According to the transfer matrix of transition pipeline, the noise at the pipe orifice, which is the output of a random white noise excitation source, is used as the output sound pressure signal to obtain the input sound pressure signal of the combined sound source system and realize the sound signal compensation of the system. The experimental results show that compared with the traditional equalizer adjustment method, this method can achieve a stable sound pressure signal output in a wide range of test frequencies and the noise signal obtained meets the test requirements. Secondly, the acoustic signal before and after the correction is used to measure the transmission loss of the expansion cavity. The measured curve after correction is in good agreement with the theoretical one, which proves the feasibility of this method.