Abstract: Aiming at the problem of thermal fatigue cracking and water leakage failure of conformal waterway die-casting mold inserts in additive manufacturing, a comparative study was conducted on the thermal fatigue resistance of three typical additive manufacturing die steel materials, 18Ni300, 12Cr9Ni, and 1Cr13, using self constrained thermal fatigue tests. The results show that thermal fatigue cracks are easy to initiate in stress concentration places such as depressions on the inner wall of the waterway, and propagate in the direction perpendicular to the thermal stress.The evaluation results of main cracks and thermal fatigue damage factors show that the thermal fatigue resistance of the 1Cr13 sample is the best, followed by the 18Ni300. 12Cr9Ni has the worst thermal fatigue resistance. There is no direct correspondence between the thermal fatigue resistance and the mechanical properties of the three materials.On the contrary, the oxidation corrosion phenomenon is always accompanied and accelerates the thermal fatigue crack growth. The formation of Cr₂O₃ oxide film can delay the crack tip growth, and the Cr element in the material becomes the major influence factor of thermal fatigue.The research results provide important experimental basis for the engineering application of additive manufacturing die-casting mold inserts.