According to the increasing demand for the steel pipe in the world nowadays, as an effective method, ultrasonic testing plays a very important role in quality controlling procedures. Compared to the mature technology of the world, the domestic one still has some technical difficulties in high-speed probe rotating mode. This paper proposes an approach of combination of multi-probe arrays based on the internal detection way to solve the difficulty of coarse pitch. The structure of the inspection system is described with the workflow laying out. The practicability and reliability of the system is verified by means of a mass of experiments. The numeric automatic ultrasonic testing system has been successfully used and the technical data is given out at last.