The invention discloses a workpiece fixing device and method for ultrasonic nondestructive test in the field of low-voltage apparatuses. The device comprises a standard clamp base and an individual clamp, wherein the standard clamp base refers to a convex cuboid; a positioning hole is formed in the bottom of the standard clamp base and is matched with a positioning pin of a detection water tank; a guide slot is formed in the bottom of the standard clamp base and is communicated with the positioning hole; a wedge-shaped table on the upper part of the standard clamp base is divided into multiple stations; connecting grooves are formed in two sides of the wedge-shaped table of the standard clamp base and are used for realizing connection between the standard clamp base and the individual clamp; the individual clamp comprises a bottom connecting structure, an adjusting structure and a positioning structure; the bottom connecting structure is of a bridge structure and is used for matching with the wedge-shaped table of the standard clamp base; the adjusting structure is in the broken line form; the positioning structure refers to a planar boss; and the positioning structure and the adjusting structure co-act, so that a to-be-detected workpiece is accurately positioned. The device disclosed by the invention is accurately positioned, and the types, number and positions of the placed workpieces can be adjusted according to needs.