The hot tearing of K418 alloy turbocharger turbine blades was investigated. The effects of aluminum and titanium content on the microstructure of K418 alloy were analyzed by optical microscope and scanning electronic microscope (SEM). The probable equilibrium phases in K418 alloy were calculated and the effects of changing of aluminum and titanium content on the equilibrium phases were studied by Thermo-Calc software. The results show that the microstructure of K418 alloy changes obviously with the aluminum and titanium content increasing. The size of γ′ and the amount of (γ+γ′) eutectic increase, resulting in more prior forming and propagating areas of the hot tearing. The hot tearing is caused by the fracture of dendrites structures, forming and propagating along the interdendrites. The precipitation temperature and mass fraction of γ′ rise with aluminum and titanium content increasing, and especially aluminum has a more important effect. The effective crystallization temperature interval is broadened with aluminum and titanium content increasing, which leads to the hot tearing of the turbine blades.