Abstract: For problems that existing condition monitoring device for three machines on mechanized mining face is bulky, difficult to install, inconvenience to maintain, and cannot online upgrade program, an intrinsic safety condition monitoring sub-station for three machines based on C8051F040 MCU was developed, and IAP technology was used to achieve online automatic upgrade of condition monitoring device for three machines. The volume of the improved sub-station is only 1/10 of original sub-station, and the improved sub-station can be connected with the existing master station and achieves online monitoring and fault diagnosis of three machines on mechanized mining face. The prototype test results show that the improved condition monitoring device for three machines on mechanized mining face runs reliably, monitors condition accurately and has ability to update programs online.