A visual inertial odometry system for multi-rotor unmanned aerial vehicle (UAV) is designed to solve the navigation and positioning problems of multi-rotor UAV in the case of interference or denial of global navigation satellite system (GNSS) signals. The overall design scheme, hardware selection and design, software system construction, communication protocol and algorithm design ideas of the system are introduced. The experimental results show that the system can actually run on the multi-rotor UAV, and when the global navigation satellite system signal is not available, it can still provide the current available pose of the multi-rotor UAV to the flight control in real time, which provides a reference for the design of vision-aided navigation of the multi-rotor UAV.