Abstract The single- or multi-variable control of full-state feedback with a full-order observer is applied to design a nonlinear Pressurized Water Reactor (PWR) core load following control system for regulating the core power level and axial power shape. A two-point based nonlinear PWR core model without boron and with the power rod and Axial Offset (AO) rod is built. The linearized single-variable (multi-variable) core model under Case 1 (Case 2) classified by two movable regions of power rod is constructed. Based on a linearized core model, the state feedback control is implemented by utilizing the robust pole assignment method with an additional integrator for Case 1 and devising an integral decoupling control system with a dynamic controller for Case 2; a Kalman filter with robustness is designed as an observer for each case. The integration of the state feedback and the observer structures a controller of the nonlinear core model of each case. For Case 1 (Case 2), the nonlinear core model and the state feedback single-variable (multi-variable) control construct the nonlinear PWR core load following control system. Finally, the control system of each case is simulated and the simulation results show that the control system is effective.