Abstract: The non-destructive testing of small sized (M12-M20) austenitic stainless steel bolts in use is always a technical problem. According to the reliability testing needs of stainless steel bolts in use, this paper analyzes sound field distribution of stainless steel bolts in ultrasonic phased array by simulation, observes its sound field coverage in ultrasonic phased array and sets inspection process parameters. Simulation analysis on and comparison of the sound field echo status of the in use stainless steel bolts in good and flawed condition, and based on the sound field calculation of stainless steel bolts phased array simulation, the paper also discusses and analyzes the effects of different pulse repetition frequency on the accuracy of detection results, and shows the method how to eliminate the false defection signal of phantom echo generated by pulse repetition frequency. Finally, by combining the process optimization method of simulating calculation and pulse repetition frequency, cracks of in service stainless steel bolts were successfully detected by applying ultrasonic phased array. It proved the accuracy of ultrasonic phased array inspection technology, which could provide technical support for future non-destructive testing of austenitic stainless steel bolts in use.