The invention relates to a blade locating device for machining a milling dowel of a compression ignition guide blade of a milling machine. The blade locating device can solve the problems that when the milling dowel of the compression ignition guide blade is machined in the prior art, the milling dowel and a blade root locating groove can be not consistent in location degree easily, the rejection ratio of products is high, production efficiency is low, and production cost is high. The device comprises a clamp plate, a blade top hold-down mechanism, a sliding locating pin, a screwing ejection mechanism, a blade root pressing plate, a draw-in bolt and a cushion block. The blade top hold-down mechanism comprises a first stand column, a second stand column, a lock bolt, a nut and a cross beam. The clamp plate is a rectangular plate. The sliding locating pin comprises a rectangular block body and a pin, the pin is horizontally fixed at the top end of the rectangular block body, and two protrusions are machined on the two corresponding sides of the bottom end of the rectangular block body. The screwing ejection mechanism comprises a plate body and a puller bolt. The blade locating device is used for machining the milling dowel of the compression ignition guide blade.