For the simulation of load-follow control operation of pressurized water reactors (PWRs), the system model needs to describe both primary and secondary system behaviors, because the load-change signal in the secondary system delivers a change in the primary system through the thermal-hydraulic interactions in the steam generator. In this study, the characteristics of load-follow control for a PWR were investigated using a one-dimensional core model combined with a simplified nuclear steam supply system model using optimization. The overall system model includes one-dimensional core neutronics with all the space-dependent feedback effects, Xe-I dynamics, core thermal balances, primary loop thermal balances, and steam generator dynamic responses to turbine load changes. The final system equations were manipulated for the lumped parameter representations by using the model expansion technique for the core model.