This paper deals with the problem of lever-arm compensation encountered in an unmanned aerial vehicle surveying system, which is composed of several surveying sensors, a position and orientation system (POS), and an electrooptical pod. As an integration of an inertial navigation system and a global positioning system (GPS), the POS is used to provide the position and attitude of the surveying sensors for motion compensation. However, the lever arm between the inertial measurement unit and the GPS antenna is uncertain and time-varying, and therefore, its influence on the estimation accuracy of POS is serious. In order to improve the measurement accuracy of the POS, a new scheme of dynamic lever-arm compensation is proposed in this paper. The main contribution of this paper is twofold. First, by using the encoder data of the electrooptical pod, a dynamic lever-arm compensation method is derived to compensate the caused lever-arm effect. Second, an H_∞ a posteriori filter is designed for POS to attenuate the influence of a lever-arm compensation error and noise uncertainty. Finally, an actual flight experiment for the transmission line corridor surveying is carried out, and it is validated that the proposed method outperforms the existing methods.