In this paper, a new variable gain PD controller design scheme is proposed, whose PD parameters are tuned corresponding to the jib length, the rope length and the jib angle. Since the jib angular acceleration is utilized as the control input, PD controller is employed which is removed the integral action from the PID controller. The PD parameters are adjusted in an on-line manner based on the pole-assignment control scheme. Furthermore, the effectiveness of the newly proposed PD control scheme is numerically and experimentally evaluated on the sway control system of a lifted load for a mobile crane.