The combination of Ni3Al-based superalloy and S31042 steel could meet service requirement of different parts in nuclear power units. To broaden the application of Ni3Al-based alloy, vacuum diffusion bonding with S31042 austenitic heat-resistant steel was studied in this work. Different thicknesses (2, 5, 10, 15, 30 ��m) of pure Ni interlayer were adopted to obtain a sound bonded joint. Result shows that the formed AlN phase in bonding process hindered atom diffusion and deteriorated joint properties. When interlayer thickness is 15 ��m, the joint strength reached 96% of Ni3Al-based alloy, meanwhile elongation was 320% of Ni3Al-based alloy and 62% of S31042 alloy. The less AlN phase, uniform precipitation of ����� phase and grain boundary intermigration behavior in two substrates contribute to the high strength and elongation of joint. The prevailing mechanism of the dissimilar joint bonded by 15 ��m interlayer is ductile fracture. However, the fracture with low elongation showed the equiaxial pot and intergranular torn edges in other bonded samples due to the typical dual-phase structure in interlayer.