The invention discloses a filter speed reducer, which comprises an eccentric shaft, a split spine half-axle dual gear, a fixed gear, an output gear and a rubber alloy layer. The split spine half-axle dual gear, the fixed gear and the output gear are helical bevel gears which are organically meshed to form a backlash-free precise transmission pair and can adaptively compensate for abrasion of tooth surfaces; the rubber alloy layer adhered on the split spine half-axle dual gear can ensure that a transmission component filters fluctuation caused by the conversion of a low speed and high torque into a high speed and low torque of a motor, processing and mounting errors and the like through a controllable elastic distortion quantity in a designed transmission accuracy and bearing capacity range, effectively prevents generation of nonlinear coupled vibration of a transmission system caused by influences of extreme working conditions and special environments, and solves the problems of generation of jam even inflexible lock and the like of the transmission component. Thus, the filter speed reducer has the advantages of high precision, high reliability, long service life, high torque, low energy consumption, small volume and the like, and can be widely applied to equipments in engineering fields, such as robots, space flights, ships and vehicles.