The present invention discloses a tool for fast detection of worm length, the tool comprises a base and a cover mounted on the base. Inner side wall of the cover is in rotatory connection with a second rotary rod through a bearing seat, lower end of the second rotary rod is in fixed connection with a fixed seat, the worm is clamped inside the fixed seat by a clamping mechanism, a scale is fixedlyinstalled on inner side wall of the cover, an oil storage barrel is fixedly installed on inner side wall of the cover, the oil storage barrel is filled with lubricating oil, and an oil outlet pipe isinstalled at bottom of the oil storage barrel. The tool can take the lead in realizing demonstration of working state of the worm through cooperation of the clamping mechanism and a simulated workingmechanism, so that detecting personnels can directly observe smoothness and occlusion tightness of meshing transmission between worm wheels and the worm through naked eyes, thereby worms that are outof specification are removed, greatly improving quality of worms leaving factory, preventing defective products from flowing into the market, and improving market reputation for enterprises to a certain extent.