The invention relates to an incomplete-teeth worm and gear reducer with limit, which comprises a substrate (1), the substrate (1) consists of a shaft housing (1.1) and a seat ring (1.2) connected together with the shaft housing (1.1), a worm (2) is arranged in the shaft housing (1.1), the seat ring (1.2) is internally provided with an output shaft (5) in a penetrating manner, the output shaft (5) is provided with a revolving worm gear (3) which is meshed with the worm (2), the revolving worm gear (3) is an incomplete-teeth worm gear, and a check block (6) is fixedly arranged on the seat ring (1.2) of the substrate (1) and positioned at non-tooth positions of the incomplete-teeth worm gear. The incomplete-teeth worm and gear reducer is simple in limiting structure, and low in design and manufacturing cost, and can effectively realize the intersection angle of a solar tracking system.