The invention provides a preparation method of an unbonded phase ultrafine tungsten carbide hard alloy. The method comprises the following steps that (1) ultrafine tungsten carbide powder is preprocessed through a preprocessing solution, and ultrafine tungsten carbide powder containing a large number of crystal defects is obtained; and (2) the unbonded phase ultrafine tungsten carbide hard alloy is prepared through a hot-press sintering or spark plasma sintering technology. According to the preparation method, the ultrafine tungsten carbide powder is preprocessed through the preprocessing solution, the large number of crystal defects such as stack fault and dislocation are created on the powder surface, the surface defect performance of the ultrafine tungsten carbide powder is improved, accordingly the sintering temperature is reduced, the density of the unbonded phase ultrafine tungsten carbide hard is remarkably improved, and excellent mechanical properties are achieved; and the preparation method is simple in process, high in maneuverability and low in cost, and scale production is easily realized.