The invention discloses a method for leveling a sediment bed surface of a large-scale wide-body water tank and an instrument erecting device thereof. A system at least comprises a large-scale wide-body water tank (14) containing sediment and water and a height-adjustable rectangular blade (17) arranged in the large-scale wide-body water tank (14) and with a level (15). The system also includes four multi-buckle measuring frames (21). The method can be used to obtain a smooth sediment bed surface with a high degree of consistency mainly by using the height-adjustable rectangular blade (17) to push a sand bed and meanwhile by using a horizontal laser (19) for positioning and calibrating the flatness of the sand bed. The multi-buckle measuring frames (21) on the other side opposite to the steel knife can ensure that a travelling crane can carry a variety of experimental equipment. The method and device of the invention can determine the flatness of the sand bed with high precision in the range of 2 mm; and can also produce an initial channel blade (16) with different width according to different experimental requirements, and has wide applicability to a laboratory water tank.