Abstract: During the operation of the Amalog-sonoscopeⅡflux leakage inspection system, some pipes detected have defects as hidden with a certain depth, and the detection wave fails to reach 50%alarm gate.This means there exist a quality risk, i.e., some defected pipes might be undetected.Briefed in the article are the operation principle and detection limitation of the flux-leakage detection process.Accordingly the solution for reducing the missing rate of sub-surface hidden defect of the steel pipe is proposed.And based on the Visual Basic program design language, the Double Gate color-catching software is developed.This software is designed with 25%or 30%level early-alarm gate so as to realize the function of double gates, i.e., the early-alarm gate and the original alarm gate during the flux-leakage detection operation.The software has such advantages as low development costs, small amount of codes, and quick response, being capable of effectively detecting deeply-hidden steel pipe defects.The actual operation of the software shows its satisfactory efficiency.