Abstract: In order to enhance the accuracy of domestic magnetic flux leakage (MFL) detector to quantify defects, the effects of defect depth, diameter and location on magnetic leakage field are simulated by producing point corrosion defects with different parameters on both surfaces of the tank bottom plate using ANSYS software. The results show similar rules of magnetic leakage fields for both surfaces: given constant defect diameter, magnetic induction components B_x and B_y increase with the defect depth; given constant defect depth, B_x hump bottom width N_x and B_y peak spacing N_y increase with the defect diameter; the defects with the same size on both surfaces present different magnetic leakage fields in distribution characteristics and size. Functional fitting of corresponding results derives a quantitative relationship between defect parameters and magnetic leakage field characteristic, providing original data reference for defect quantification.