Abstract: With VB 6.0 as a platform, the adjustment of sensitivity in the automatic ultrasonic testing (UT) of round-stick workpieces using R0B65VIS automatic testing equipment was simulated. According to the features of the sound wave spreading process in UT, its mathematical model and main principle were extracted, which realized the simulation of the sensitivity adjustment in automatic UT of round-stick workpieces. This thesis solved two basic problems, complicated calculation due to the various parameters in the sensitivity adjustment of round-stick workpiece testing and difficulties in judgment of the artifical flaw resulted from tail-wagging of the stick material in automatic testing. This simulation modeling was generally applicable for all purposes, which provided theoretical instruction for the sensitivity adjustment in practical testing.