Abstract: In order to get the quantitative geometry of defect, based on the introduction for the principle of pipeline magnetic flux leakage, firstly a two-dimensional magnetic flux leakage signal was simulated by ANSYS software. It showed the basis characteristics of pipeline magnetic flux leakage defects signal and put forward the corresponding interpretation. Secondly, a contrast between internal and external defects magnetic flux leakage signal was made and the right two features were put forward. Finally according to the change law between the different features of magnetic flux leakage and the defects length, the quantification of defects length was completed. Through the comparison of different quantifying models, it made a general model of defects signals features and defects length, providing relevant parameters for the assessment and the prediction of strength and remaining life of pipeline and thus leading to proper maintenance for the pipeline.