This paper presents a new approach based on the method of magnetic flux leakage (MFL) for the double-sided butt weld (DSBW) of the welding equipment such as the pressure vessel in order to detect and identify the weld defect. In this approach, a new magnetization structure is adopted whose magnetization direction is perpendicular to weld line, also, a new continuous non-contact scanning method is used, what aims to solve the problems about complex leakage magnetic field (LMF) space distribution. Then, the LMF distribution laws with non-defect (ND) and laws with precrack from heat affected zone (PFHAZ) are obtained through using these methods such as theoretical analysis, numerical simulation, and experimental study. Afterwards, this paper reviews the recognition analysis of the above-mentioned two kinds of state (ND and PFHAZ) by binding the contrastive curves. The outcomes indicate that the suggested method of MFL has realized the recognition of ND and PFHAZ; The numerical simulation results and experimental results match each other well and their correlation coefficient R is 0.9729. Furthermore, the results verify the feasibility and the validity for the suggested method. This is a new way for exploration detection of the double-sided butt weld.