This paper presents a wireless clamp-on torque sensor based on dual or quad one-port SAW resonators to meet the measurement requirements of transmission system. Firstly, the principle of clamp-on torque sensor is introduced, the mechanical model of the structure is calculated and simulated by theoretical analysis and COMSOL. The differential measurement method is confirmed, and the optimal structure parameters are studied. Then, the torque sensitive theory of SAW devices is analyzed, the differential SAW torque sensing elements and the measurement system are designed based on the frequency division multiple access (FDMA). And a novel sensing element installation method is proposed, which reduces the installation error influence on sensor accuracy. Finally, the clamp-on structure prototype and measurement system are verified by the static calibration experiment. The results show that: the torque sensor has the capability that 1.931 KHz/Nm of sensitivity under ±100 Nm with good linearity and consistency. The torque sensor has the advantages of wireless, non-contact, easy installation, high reliability, and easy maintenance, it is suitable for the torque measurement of transmission system.