With the rapid development of automotive industry, the requirements for engine performance hasbecome increasingly higher and higher, such as dynamic performance, environmental performance, fuel economyperformance and so on. Obviously, using lighter aluminum engine has become the future of the automobile industry.When start or stop the engine, the engine generates drastic temperature field that will make parts of the enginecomponents into the plastic deformation zone. If the engine components continue like this, extremely high thermalstrain will cause the thermal fatigue failure of aluminum alloy for automotive engine. Thermal fatigue is a more seriousform of material fatigue failure. The thermal fatigue is prevalent in many important engine castings, such as cylinderbody, cylinder head, piston and so on. Therefore, study on thermal fatigue properties of multivariate Al-Si-Cu castalloy has the most important significance. Based on this thermal fatigue behaviors of multivariate Al-7.5Si-4Cu alloys under different heat treatmentwere investigated in the temperature ranges of room temperature to 350℃. Thethermal fatigue cracks of the tested specimens were observed using OM and SEM. The results demonstrate that thermalfatigue properties of the alloy after T6 heat treatment is better than the alloy after cast-quenching+aging heattreatment and the cast alloy. Reasonable heat treatment process can improve the strength, the plasticity and thethermal fatigue property of multivariate Al-7.5Si-4Cu alloy, including reduce the rate of crack propagation.The main reason of crack initiation is oxidative microstructure induced by thermal stress. Fatigue crack expands alongthe grain boundary bypassivation-sharpen of crack tip in the early. In the late, fatigue crack expands with both intergranular way andtransgranular way by passivation-sharpen of crack tip and siamesed holes on front edge of crack tip. The Si phasescan affect fatigue crack propagation. When the angle between the fatigue crack propagation and the short axis of theSi phase is more than 60°, fatigue crack expandsas “bypass-wall expansion”. When the angle between the fatiguecrack propagation and the long axis of the Si phase is more than 60°, fatigue crack expands as “through-wallexpansion”. Oxidation behavior effects significantly at the crack initiation period. After T6 heat treatment, theantioxidant property of multivariate Al-7.5Si-4Cu alloy is the best. Oxidation kinetics curves of multivariateAl-7.5Si-4Cu alloy under the different heat treatment are all logarithmic relationship.