The invention relates to the field of design of an assembly clamp/mould and relates to a device for accurately controlling thickness of a laser fused preset powder layer. A screw rod (8) is vertically fixed on a base (9); the upper end of the screw rod (8) is screwed into a horizontally arranged disc-shaped spiral pipe (7); a disc type sleeve pipe (4) is arranged above the spiral pipe (7); a coaxial structure for keeping the spiral pipe (7) and the sleeve pipe (4) coaxial is arranged between the spiral pipe (7) and the sleeve pipe (4); a powder pore cavity (4b), of which the shape size is as same as that of a substrate material plate (3), is arranged at the center of the sleeve pipe (4); a gasket (5) is arranged in the powder pore cavity (4b); a horizontal projection of the gasket (5) is contained in the powder pore cavity (4b); the substrate material plate (3) is arranged in the powder pore cavity (4b); powder (2) is paved on the substrate material plate (3); a metal press head (1) is pressed above the powder (2); and the shape size of the horizontal projection of the metal press head (1) is as same as that of the substrate material plate (3). The device provided by the invention has the advantages of simple structure, easiness in operation, continuous adjustable powder-paving thickness, high precision and special suitability for technical study experiments.