The invention discloses a power transmission line composite insulator water diffusion test sample preparation precision cutting tool. The tool comprises a tool body composed of an aluminum profile anda stainless steel plate, a push bench, a motor, a saw blade and a saw blade position dust cover. The push bench comprises a pneumatic positioning clamp, an adjustable pneumatic positioning clamp, a positioning clamp position dust cover, a vacuum cleaner interface, an optical axis, a screw rod, a slide rail, a push bench plate, a cylinder manual valve, a guide rail slide block, a screw rod hand-cranking wheel, an optical axis slide block and a screw rod slide block. The pneumatic positioning clamp is composed of a lower fixing plate, a V-shaped block, a side surface supporting plate, a cylinder and an upper fixing plate. A workpiece is placed on the V-shaped block of the two pneumatic positioning clamps, and is parallel to the push bench plate and parallel to an axial direction of a motormain shaft. One-time sampling can be performed, a lot of polishing time can be reduced, and harm of dust to an operator and the environment around a machine is decreased.