The invention relates to a transmission assembly. The transmission assembly comprises a transmission shaft, a reciprocating moving part and a sliding way. A left-handed rotation cylindrical spiral groove and a right-handed rotation cylindrical spiral groove are symmetrically formed in the lateral surface of the transmission shaft and are connected in an end-to-end mode to form a closed loop in the smooth transition. The reciprocating moving part is installed on the sliding way parallel with the axis of the transmission shaft and is combined with the spiral grooves in the transmission shaft, so that the reciprocating moving part travels along the spiral grooves along with rotation of the transmission shaft and moves in a reciprocating mode along the sliding way; the reciprocating moving part comprises a rolling column; the axis of the rolling column keeps perpendicular to the axis of the transmission shaft; the lateral face of the rolling column is in rolling combination with the lateral walls of the spiral grooves. The roughness Ra of the lateral walls of the spiral grooves ranges from 0.4 micrometer to 1.0 micrometer. The invention further relates to a transmission device comprising the transmission assembly. The transmission device further comprises a gear transmission and unlocking device, a connection rod and a crankshaft. Large torque can be transmitted, continuous transmission is achieved by overcoming the self-locking characteristic of a screw rod, inertia force of an output shaft can be used for power input to a certain extent, and energy is saved greatly.