The invention relates to the technical field of metallurgy, in particular to a preparation method of an equal-thickness ultrafine grain TC4 titanium alloy plate. The preparation method comprises the steps that S1, plate blanks obtained after rolling and annealing are taken; S2, the plate blanks are grouped; S3, interfaces of the plate blanks are subjected to roughening treatment and cleaning, and then the following operation of S4 is executed on each group; S4, the plate blanks in each group are stacked into a plate layer, one side edge of each plate layer is welded, the other side edges of each plate layer are coated with anti-oxidation coatings, or all edges of the plate layers are subjected to vacuum seal welding, the hot rolling process is adopted for ply rolling and welding, final hot rolling is carried out till the thickness of the plate layers is equal to the original thickness of the plate blanks, and then air cooling is carried out; S5, if the plate layers need to be grouped again, the plate layers serve as new plate blanks to return to the step S2, and otherwise all the plate layers form a plate blank group to return to the step S3 till all the plate blanks are subjected to ply rolling into the plate; S6, the plate is subjected to heat treatment and then cooled. According to the method, the defects of the insufficient hot rolling deformation and deformation cracking and incomplete welding in the ply rolling process can be overcome, and the equal-thickness ultrafine grain plate can be prepared.