A deceleration mechanism comprises a base, a transmission device rotatably connected to the base, and a driving device fixed to the base. The transmission device includes a driving assembly having a driving wheel and a driven assembly having a driven wheel. Diameter of the driven wheel is greater than that of the driving wheel. The driving device provides power to rotate the driving wheel. The transmission device further includes a transmission member wound on the driving wheel and the driven wheel. The transmission member winds on the driving wheel at least one winding, then criss-crosses and winds on the driven wheel.