Precision multi-section type planetary speed reducer

The utility model discloses a precision multi-section type planetary speed reducer, which comprises a casing, a first planetary gear, a second planetary gear, a third planetary gear, a bearing seat, a bearing, an output shaft and a cylindrical protecting casing, wherein a back end cover is arranged at the lower part of the casing through a screw, a front press cover is arranged at the upper part of the casing, and is in sealed connecting with the casing through a flange, the casing, the back end cover and the front press cover form a working cavity of the speed reducer, and the bearing seat is arranged at the upper part of the working cavity. The precision multi-section type planetary speed reducer has the advantages that by utilizing the matching of multiple planetary gears with planetary bearings, the speed reducer can meet the requirements of lower rotation speed and higher torque, the friction between the gears and a gear shaft is greatly reduced, and the accuracy of the device is improved; the speed reducer is arranged on the large equipment through the cylindrical protecting casing which sleeves the exterior of the casing, the influence of vibration on the speed reducer is reduced, and the accuracy of the speed reducer is further improved; the impact force is reduced, and the damage probability is reduced.