The invention relates to a preparation method of an alloy, in particular to an ultrafine grained Ni-Al alloy, which solves the problem that the Ni-Al alloy prepared by the prior art has low density and poor mechanical property. The method comprises the steps of: 1. mechanical alloying; and 2. sintering in a vacuum hotpressing way to obtain the ultrafine grained Ni-Al alloy. The prepared ultrafinegrained Ni-Al alloy has average crystal grain size of about 400nm and Vickers hardness average value of 450; compared with as-cast state coarse-grained Ni-Al alloy, room temperature strength of the ultrafine grained Ni-Al alloy is improved greatly by about 800 MPa; and meanwhile, the room temperature dependent variable is improved to 9.5% from 5%.