Speed reducer based on cylindrical roller bearing

The invention discloses a speed reducer based on a cylindrical roller bearing. The speed reducer based on the cylindrical roller bearing comprises a main shaft, planetary gears, cam shafts, first cylindrical roller bearings, a shell and cycloid needle wheels; the shell is of a hollow cylindrical structure, and the main shaft is coaxially arranged in the geometric center of the shell; the three camshafts are arranged on a circle with the main shaft as the center in parallel with the radian of the main shaft; one planetary gear is fixedly arranged at the lower end of each cam shaft, gears are fixedly arranged at the lower end of the main shaft, and the gears are meshed with all the planetary gears; two first cylindrical roller bearings are fixedly arranged on each cam shaft in a sleeving mode, two cycloid needle wheels are arranged on the main shaft in a sleeving mode, and holes are formed in the positions, located on the cam shaft, of the cycloid needle wheels, the cam shaft penetratesthrough the corresponding