Porous NiCrMoCu alloys were fabricated by reactive synthesis sintering technique with Ni, Cr, Mo and Cu element powders as raw materials. Phase composition, the volume expansion ratio, pore structures and pore morphology were characterized and the pore forming mechanism was discussed. The results indicate that the pore size, porosity and volume expansion rate of porous materials increase with the increase of Cr amount. When the Cr content is 30 wt%, the open porosity reaches 42.10%, the total porosity is 48.36%, the volume expansion rate is 12.60%, the average pore size and permeability are 13.32 μm and 96.3 m³?m^-2?kpa^-1?h^-1, respectively. The diffusion rates of Cr, Mo, Cu atoms in different matrix elements at 1150 ℃ are calculated, and the calculation results illustrate that the diffusion rates of Cr atoms in Ni and Cu atoms are 1.61×10^-14 m²?s^-1 and 8.22××10^-13 m²?s^-1, respectively, which is higher than the diffusion rates of Mo and Cu atoms. The pore forming mechanism is explored and it is mainly based on the inter-connected pores in the green compacts and the Kirkendall effect due to the different diffusion rates of Cr, Mo and Cu atoms in the nickel substrate.