Al matrix composites (AMCs) have been used in the aerospace and automotive industries due to the desirable properties including high specific strength, superior wear resistance and low thermal expansion. However, the traditional fusion welding process of AMCs usually brings defects such as pores, particles segregation and detrimental phases, which limits the application of AMCs. So more and more attentions are paied on friction stir welding (FSW), a solid state welding method possessing great potential in the welding of AMCs. In this work, to acquire high quality and excellent fatigue property of friction stir welded SiC_p/6092Al composite joint, 3 mm-thick rolled SiC_p/6092Al composite plates with T6 state were conducted by FSW at a constant rotational rate of 1000 r/min, and at a low welding speed of 50 mm/min and a high welding speed of 800 mm/min, respectively. Microstructure evolution, mechanical properties and high cycle fatigue behavior of the FSW joints were evaluated. The results showed that high welding speed resulted in a much rougher surface of scale-like ripple and the morphology of the nugget zone was different from that of the joint at low welding speed. Significant enhancement of the hardness and tensile strength were achieved in the joints at the high welding speed, but the fatigue properties were not improved for the joints with unpolished surfaces. The fatigue limit of the joint at low welding speed was 150 MPa, however the fatigue limit reduced to 140 MPa at the high welding speed. For the joints with polished surfaces, obviously enhanced fatigue limit was achieved at the high welding speed of 800 mm/min compared to that of the joint at the low welding speed of 50 mm/min. Different fracture characteristics were observed in the specimens with unpolished surfaces at various cyclic stress loading. Under a low cyclic stress loading, crack initiated at the scale-like ripple on the surface of the specimen; under a high cyclic stress loading, crack also initiated at the scale-like ripple at the low welding speed, while the crack initiated at the swirl zone in the bottom of the nugget zone at the high welding speed. The results of three-dimension surface topography showed that a large surface roughness was achieved on the surface of the joint at the high welding speed, resulting in lower fatigue limit compared to that of the joint at the low welding speed. For the specimens with polished surfaces, the fatigue limit was improved by 40~65 MPa compared to that of the specimens with unpolished surfaces. In this case, a high fatigue limit of 205 MPa was obtained in the joint at the high welding speed of 800 mm/min, and all the specimens failed at the lowest hardness zone and nearby.