To validate the performance of the optical system of the tested equipment, the airborne multi-light source steering device needs to track the mounted equipment on other aircraft during flight tests and provide it with five beacon lights with a maximum span of more than 2 meters and parallelism less than 0.3°. The design, calibration, and flight environment of the airborne multi-light source steering device can affect its pointing accuracy. To address this issue, this paper studies the pointing accuracy of the device, separates its errors, and proposes a method based on the combination of multi-body system theory and finite element simulation. By establishing a mathematical model of pointing errors and relying on finite element simulation to simulate real-world working conditions, the dynamic pointing error patterns are analyzed. Finally, the method is validated through experiments. In the ground dynamic tests, the device's pointing accuracy is 0.2099°, and during the flight tests, the pointing accuracy is 0.231° with an accuracy rate of 90.86%. This proves that the proposed method is highly reliable and accurate.