In order to improve the accuracy of orientation when unmanned helicopter is in autonomous flight and operation,a measurement system that could fetch flight states relative to mission target is designed. In the system,an airborne lidar is used to scan and model the surroundings,and a hardware circuit based on STM32 microcontroller is designed to realize all functions. Also,a specific algorithm that can process and analyze surroundings data and work out the states of unmanned helicopter is proposed. By a software programmed by Labview,flight states measured by the system can be displayed in real time. The experimental results prove that the measurement system can fetch the distance and azimuth of the unmanned helicopter relative to the mission target accurately.