The failure of rolling bearing in the running process may cause serious consequences, so it is of great significance to carry out on-line detection of bearings. A portable bearing fault online detection system based on STM32 and FPGA is designed to solve the problem of on-line detection of rolling bearings. In terms of hardware, the FPGA chip is used as the data processing unit to realize the A/D conversion and on-line acquisition of bearing vibration signal, and the signal noise reduction, envelope spectrum analysis and fault frequency extraction are carried out. The bearing vibration signal time domain waveform and fault spectrum are displayed in real time by LCD screen. The STM32 single chip microcomputer is used to design the system UI control interface, control the sampling rate, waveform display and display the diagnosis result, and realize human-computer friendly interaction. In the aspect of algorithms, adaptive line enhancement technology is implemented by FPGA to reduce the noise of the collected signals, and the fault spectrum is obtained by envelope spectrum analysis and the fault characteristic frequency is extracted. Finally, the system is tested by the self-built mechanical integrated fault simulation test bench. The experimental results show that the system can effectively extract the bearing fault frequency, and the speed is improved by about 30 times compared with the software detection scheme, which can meet the requirements of online detection.