The invention discloses a preparation method for B4C/Al composite material boards, and belongs to the technical field of composite material preparation. The preparation method comprises the steps of mixing raw material powder, preparing and extruding initial blanks and carrying out extruding formation of the boards. According to the invention, the processing procedures can be greatly reduced, the utilization rate of raw material can be greatly increased, and the production cost can be lowered. The prepared B4C/Al composite material boards are good in compactness and excellent in mechanical property and capacity of absorbing thermal neutrons, the tensile strength can reach 280 MPa, and the rate of absorbing the thermal neutrons by the composite material boards with the thickness being 5 mm can be higher than 90%.