Abstract: Due to its inherent safety feature, high temperature gas-cooled reactor (HTGR) has been seen as one of the best candidates for the next generation of nuclear plants. The safe, stable and efficient operation are necessary to the development of HTGR technique. Power-level control technique that strengthens both the closed-loop stability and transient response by properly generating the insertion or withdrawal speed of the control rods is beneficial to improve the operation performance of HTGR. In this paper, through the physically-based approach, it is proved theoretically that proportional-differential (PD) output feedback laws can provide globally asymptotic stability (GAS) for the closed-loop system if a sufficient condition is satisfied. The numerical simulation results verify the theoretic results, and show the influence of different PD feedback gains to the regulation performance. The results guarantees that classical PD output feedback control is effective for HTGR power-level regulation practically, and also shows the feasibility of applying simple PD control for load following function.