Abstract: The on-line automatic ultrasonic testing(UT) system for steel pipe based on the virtual instrument is proposed through combining the design concept of virtual instrument with the conventional ultrasonic testing method in currently. The detection system was introduced from three aspects: mechanical design, electrical control and ultrasonic testing instrument. The development cycle of the ultrasonic testing instrument is short with high efficiency. The software programming is flexible and can be improved when needed. It has laid the foundation for graphical display of pipe on-line automatic ultrasonic testing.