The invention provides a sound emission method and system for judging lithology of different layers in an engineering field; the sound emission system comprises a loading system, a combined rock massand a monitoring system; the loading system is used for generating axial pressure on the combined rock mass, so that the energy inside the combined rock mass is transmitted out of the combined rock mass in the form of an acoustic wave; the combined rock mass is in a cuboid shape, and the combined rock mass is uniformly divided into three layers in the height direction; and the monitoring system isused for monitoring the acoustic wave emitted in the combined rock mass and analyzing the characteristics of the rock mass according to the acoustic wave characteristics. According to the sound emission method and system in the invention, the phenomenon that the rock mass is cracked and evolved to generate sound emission in the loading process is utilized, the monitoring system is adopted for analyzing the waveform of the sound emission wave, and the lithology of the rock masses at different positions is reflected according to the waveform signals; according to the method and the system in the invention, autonomous programming software is adopted, the original time domain data of sound emission is transformed into a two-dimensional power spectrum graph, and therefore the main frequency value of sound emission is observed more intuitively; and the equipment required for the method for judging lithology provided by the invention is simple, the work amount is small, the cost is saved, and the accuracy is high.