The invention provides a wind tunnel test platform's transmission mechanism, which comprises a main motor (4), a power decomposer (2) and a rotor driving mechanism. The rotor driving mechanism comprises an angle decelerator (7), a rotor decelerator (9) and a rotor transmission shaft (10). The main motor (4) drives the power decomposer (2) to move in pace. The power decomposer (2) drives the angle decelerator (7) to move in pace through a first transmission shaft (6). The angle decelerator (7) drives the rotor decelerator (9) to move in pace through a second transmission shaft (8). The rotor decelerator (9) drives the rotor transmission shaft (10) to move in pace. According to the invention, with the angle decelerator and the rotor decelerator, two kinds of decelerations are available and the power outputted by the main motor is transmitted to the rotor transmission shaft through the movement in pace of the power decomposer, the angle decelerator and the rotor decelerator. Further, the rotor transmission shaft is also driven to move in pace. While the structure of the mechanism is simple enough, the reliability of transmission performance is outstanding.