The utility model provides a rotation cycloidal pin wheel speed reducer, includes flange base, slewing bearing, cycloid wheel, needle tooth, eccentric input shaft and output pin, input shaft hole, needle perforation have been seted up on the flange base, slewing bearing comprises outer lane, inner circle and the steel ball and the spacing block of setting between outer lane and inner circle, circle in the slewing bearing and offered the pinhole, the cycloid takes turns to has seted up eccentric input shaft hole and pin hole. The utility model discloses using slewing bearing to combine the cycloidal -pin wheel principle for relying on, having born axial force, radial force and overturning moment simultaneously, compact structure, transmission are steady, high transmission efficiency, vibratoty noise is low, output torque is big, the one -level is slowed down, and the speed reducing ratio is big down, compares with other reduction gears with power, and weight volume reduces more than 13,small in size, and occupation space is few.