Abstract: Objective To promote lap interface to undergo sufficient deformation and achieve high-strength friction stir lap welded (FSLW) joints, a design concept of a high-angle threaded stirring pin was proposed to achieve effective joining of aluminum/steel dissimilar material joints. Methods FSLW test was conducted on 4 mm-thick 5083 aluminum alloy and E36 steel. The study focused on influence of different thread lead angles on interface formation characteristics and mechanical properties of joints under the condition that four high-angle (40°, 50°, 60°, 70°) threaded stirring pin was slightly plunged into the lower steel plate. Results As the thread lead angle increases, excessively strong material flow partially breaks steel interlocking structure, which makes mechanical interlock dimensions on both sides of stirring pin first increase and then decrease. Conclusion Structural characteristics of lap interface determines failure load of lap joints. With the increase of thread lead angle, variation law of joint failure load is related to mechanical interlocking. In shear fracture mode, shear performance of joints with high-angle threaded stirring pin is higher than that of ordinary threaded stirring pin. When thread lead angle of stirring pin is 50°, failure load of aluminum/steel FSLW joints reaches the maximum value of 6.22 kN.