The tilt-rotor unmanned aerial vehicles have an obvious trend of multi-rotor development, and modular design of tiltable rotor system helps to integrate assembly and reduce design duplication. In this paper, a quad tilt-rotor unmanned aerial vehicle (UAV) is targeted, and the modular design concept is applied to the design of the tiltable rotor system. Firstly, the modular mechanical structure, control structure and communication structure of the tiltable rotor system are designed. By using CAN bus communication mechanism designed, the tiltable rotor system is connected to the overall distributed control system as a node. Then, the internal pitch control, rotor speed control and rotor tilting control of the tiltable rotor system are studied. Finally, a tiltable rotor system test platform is built to verify the correctness of each component design of the tiltable rotor system modular components and the feasibility of the modular design concept. The results show that the rotor speed fluctuation error is less than 2.6%, the smooth and uniform transition from helicopter mode to fixed wing mode can be achieved within 7s, and the system has good real-time data communication, which meet the application requirements of tiltable rotor system. The modular design of tiltable rotor system can provide technical means and ways for the development of quad tilt-rotor UAV.