In recent years, * * * axis twin-rotor UAV has been widely used in military and civilian fields. Compared with the conventional UAV, the twin-rotor UAV with * * axis has the advantages of strong bearing capacity, high hovering efficiency, long battery life and compact structure, and has broad application prospects. However, from the current research results at home and abroad, most of the * * * axis UAVs are large in overall size and weight and poor in portability. Therefore, it is necessary to research and design a small * * * axis twin-rotor UAV. In this paper, the overall structure and layout of a small * * * axis twin-rotor UAV are studied, aiming at designing a small * * * axis twin-rotor UAV that is easy to carry. The specific research contents are as follows: (1) The design process and technical indicators of the small * * * axis twin-rotor UAV are formulated; Through the comparative analysis of three control schemes, the dual-motor differential control scheme is determined. Then the overall scheme of UAV is designed, which is divided into six subsystems, and the functional requirements of each subsystem are defined, and the overall layout design of UAV is completed. (2) establish a rotor load model and determine its maximum total pitch and rotation speed; CFD (Computational Fluid Dynamics) method is used to simulate and analyze the loads with different rotor spacing, and the optimal rotor spacing is determined. The power required by the rotor and the whole machine is determined by integral method. The structural design of the rotor system and the strength check of the main components are completed. (3) The function analysis, module division and structure design of the manipulator are carried out, and its kinematics model is established. The dimension optimization and workspace analysis of the lower manipulator are completed. The results show that the designed manipulator can meet the requirements of its workspace movement. (4) The structural design of each subsystem of UAV is completed, and the strength of important components is checked. Based on ADAMS software, the motion and mechanical characteristics of the control mechanism are simulated and analyzed. The virtual prototype model of UAV is completed. (5) The prototype of a small * * * axis twin-rotor UAV is completed, and its flight dynamics equation is established and solved based on the prototype, which makes preparations for the design of UAV flight control system in the future.