Additive manufacturing enables processing of functionally graded materials (FGMs) with flexible spatial design and high bonding strength.A steel-copper FGM with high interfacial strength was developed using laser powder bed fusion (LPBF).The effect of laser process parameters on interfacial defects was evaluated by X-ray tomography,which indicates a low porosity level of 0.042 ％ therein.Gradient/fine dendritic grains in the interface are incited by high cooling rates,which facilitates interface strengthening.Multiple mechanical tests evaluate the bonding reliability of interface;and the fatigue tests further substantiate the ultrahigh bonding strength in FGMs,which is superior to traditional manufacturing methods.Mechanisms of the high interfacial bond strength were also discussed.