Abstract: An essential issue in the application of liquid metal blanks in thermal nuclear fusion reactors is the additional magnetohydrodynamic (MHD) pressure drop caused by the interaction of the liquid metal flow with a strong magnetic field. The additional MHD pressure drop is much higher than hydrodynamic pressure drop. Argonne liquid metal experiment (ALEX) group in Argonne National Laboratory of American studied the MHD effect of Liquid Metal flow in ducts and pipes subjected to a fringing magnetic field by experiments. The experiments were introduced as one of the benchmark cases to test numerical codes for liquid metal blankets. As the liquid metal blankets would be subjected to the magnetic field with different directions, liquid metal flow in a square duct subjected to an inclined fringing magnetic field has been numerically studied in this paper. The model is based on one of the ALEX's experiments. With constant Hartmann number, Reynolds number and wall conductance ratio, the effects of the angle between the magnetic field and the side wall on the velocity, the electric current, and the pressure distribution have been investigated using three-dimensional direct numerical simulation method. The results show that the distribution of the velocity, the electric current and the pressure on the cross section rotates with the increase of the inclination angle of the magnetic field. In the uniform part of the inclined magnetic field, the velocity jets located at the junction corners of the Hartmann layer and the side layer which are parallel to the external magnetic field. The pressure gradient in the part of the uniform magnetic field increases firstly and decreases with the increase of the inclination angle of the magnetic field. In the decreasing part of the inclined magnetic field, the high-speed velocity jet is transferred to another pair of corners due to the three-dimensional MHD effect along the streamwise direction. The three-dimensional MHD pressure drop at the cross-section of the duct increases with the increase of the inclination angle of the magnetic field. Furthermore, the maximum value of the velocity jets decreases, the second flow increases and the laminar-turbulent transition of the duct flow occurs.