The acoustic emission detection technology has used widely, and the good sensitivity of the acoustic emission instrument system is an important guarantee for the acoustic emission detection. In this paper, a set of sound source signal detection platform is built, and the response characteristics of acoustic emission signals of two different sound sources in a circular steel plate are studied through experiments and numerical analysis. The experimental results show that with the increase of the distance from the sound source, the variation trend of the response amplitude of the signal in different directions is basically the same, and the difference of the response amplitude between different directions is mainly distributed in 2.1~8.8 dB. When the distance from the sound source is 0~350 mm, the overall decrease of the signal response amplitude is faster, and the signal attenuation rate of the pulse excitation is about 3% lower than that of the lead-break excitation. The sound source generated by the pulse signal excitation sensor has better stability and reproducibility. This study provides a reference for the selection of the sound source in the sensitivity test of the acoustic emission instrument.