The present invention discloses an acoustic emission sensor, including an acoustic emission probe, a probe installation mechanism, and a transmission mechanism transmitting a combination of the acoustic emission probe and the probe installation mechanism to a setting position in a borehole of a monitored rock mass; the probe installation mechanism includes a shell, a probe sleeve, a spring sleeve, a spring, and a fixed pulley component; the probe sleeve is installed in the guide cylinder of the shell, the spring sleeve is fixed on two sides of the probe sleeve, the spring is installed inside the spring sleeve; one end of the first rope in the fixed pulley component is fixedly connected to the end cap in the upper end surface of the probe sleeve through the fixed pulley mounted on the top of the inner wall of the shell.