In order to meet the demand of monitoring for axial stress in high-strength bolts of wind turbine under complex loads, an on-line monitoring system for axial stress in bolts of wind turbine was designed and implemented based on acoustic elastic effect and embedded technology. The system consists of ultrasonic transducers, embedded devices based on ZYNQ and remote monitoring computer. The level comparison method and the maximum peak-zero cross point method are used to calculate the ultrasonic time-of-flight in the bolt. And and a stable and reliable network communication protocol was established based on TCP / IP protocol to ensure the safe and reliable transmission of monitoring data to the remote monitoring computer. Experiments show that the system can realize monitoring of ultrasonic time-of-flight and stress of multi-bolts in real time, and found the problem of loose bolts, which provides technical support for remote fatigue monitoring of wind turbine bolts.