Abstract: Direct current magnetic flux leakage flaw detector is widely used in steel pipe automatic testing, and its performance directly affects the accuracy of testing results. Currently, the evaluation is primarily conducted through comprehensive performance testing of equipment (flaw detectors, sensors, mechanical components) both domestically and internationally, with no established calibration standards for the instrument performance of direct current magnetic flux leakage flaw detector. By introducing the significance of implementing calibration for direct current magnetic flux leakage flaw detector, the paper analyzes the working principle of flaw detector and the composition of its hardware, and concludes the key components that affect the performance of direct current magnetic flux leakage flaw detector, including magnetization device, attenuator (or amplifier), overall noise, and demagnetizer. Meanwhile, scientific and reasonable tools should be used to test these key parts and provide corresponding metrological parameters: relative error of magnetization current, attenuation error of attenuator, electrical noise level, and residual magnetic induction intensity. Through research and analysis, certain quantitative indicators should be proposed for the metrological parameters and effective calibration methods should be established, aiming to provide a reference for the calibration of direct current magnetic flux leakage flaw detector for steel pipe testing.