Abstract: The inspecting equipment of oil-well tubing based on the method of magnetic flux leakage(MFL) was designed. The system structure and data acquisition hardware based on USB(universal series bus) were stated. High volume and continuous data acquisition were performed by multi-thread technology. The visual data processing software and software structure was designed based on the Windows. The analysis procession to defect of oil-well tubing was described. Practical application of this system showed that it was superior on high testing sensitivity, quantitative analysis ability and simple structure and so on.