Abstract: TMCP steel is widely used in offshore steel structures at present as its well strength and toughness. The acoustic property of TMCP steel is changed because of the grain size variation during the rolling process. This article introduces the influence to ultrasonic testing by TMCP technology, and also suggests the solution to amend the influence to achieve the accurate inspection for weld seam. The solution is based on the three ways, such as making the TMCP reference block, the calibration of ultrasonic equipment and adjusting in field application.