Abstract: A 5 mm thick A356 aluminum alloy plate was welded by friction stir welding with a taper single-pin and cylindrical double-pin stirring heads. The surface forming, metallographic structure, mechanical properties and fracture morphology of the joints at different welding speeds were analyzed. The results show that the tunnel defects exist in the cross sections of the cylindrical double-pin tool joints to varying degrees, while the tunnel defects only appear at the cross section of the taper single-pin tool joint at the welding speed of 130 mm/min. The grain refinement of the taper single-pin tool mixing head is more obvious with the increase of the welding speed. The maximum tensile strength of the taper single-pin stirring head joint reaches 85% of the base metal strength, while that of cylinder double-pin stirring head joint is only 78% of that of base metal. The minimum hardness of the single-pin and double-pin stirring head joints all appear near the junction between the heat affected zone and the base material. The fracture mode of the joint prepared by using cylindrical double-pin stirring head is a mixed fracture mode of ductile fracture and brittle fracture, while the fracture of the joint prepared by using taper single-pin stirring head is a transgranular brittle fracture.