A preparation method for slab of polycrystalline diamond compact bit is provided, which comprises the procedures as follows: the preparation of moulds and preparation of raw material of slab based on the prescription are carried out, then the prepared raw material of slab is fed into the horizontal tools, the top of which is added with a proper amount of adhesive metal, which undergoes sintering before the mould is opened, wherein, the compositions by weight percentage of the raw material of slab are as follows: the cast tungsten carbonized with the granularity is of 60-100 sift (36 percent), the cast tungsten carbonized with the granularity is of 100-140 sift (25 percent), the cast tungsten carbonized with the granularity is of 140-230 sift (9 percent), the cast tungsten carbonized with the granularity is of 230-400 sift (18 percent), and pulverized nickel powder (12 percent). The preparation method provided by the present invention permits the possibility to ameliorate the efficacy of the slab of the PDC bit.