Abstract: A method combining creep wave and longitudinal wave was adopted by this paper for the complicated structure character of the component of cinquefoil bore. The ultrasonic automatic on-line testing system for the component of cinquefoil bore was developed, and the determined quantitative testing for the component flaw of cinquefoil bore was accomplished through the amalgamative mode of multi transducer. The test was performed for the artificial flat bore(diameter 0.8 mm, depth 3 mm) and the natural crack located at the step. Results showed that better testing effect could be acquired using axis, vertical and circle transducer, and the requirement of the system design was achieved.