Abstract: With the rapid development of space exploration technology and expanding space application demands, major global powers have initiated key technological breakthroughs, particularly for critical enabling technologies such as space power systems. Conventional space power devices, including solar photovoltaic and chemical power sources, fail to meet the new requirements of modern space exploration. Space nuclear power system (SNPS), characterized by high power density and minimal susceptibility to external environmental factors, have gradually become the primary energy solution for future space missions. Precise load-following capability and robust anti-interference performance are essential for SNPS operation in complex and dynamic space environments. While simulation modeling and thermodynamic analysis of Stirling cycle-based SNPS have been well-established, research on control strategies for such systems is still limited. The PID control principle is a widely adopted control method featuring simple structure and high stability. Therefore, this paper investigated control strategies for Stirling cycle-based SNPS. A thermodynamic model of SNPS was first developed, comprising a lithium-cooled fast reactor (LFR), Stirling generator, radiation radiator, and connecting pipelines. Based on the system architecture, the mathematical-physical model integrated three fundamental equations: point-reactor neutron kinetics equations (describing fission chain reactions), core heat conduction equations (governing thermal behavior) and Stirling generator dynamics equations (characterizing power conversion). Simulation modeling was conducted on the MATLAB/Simulink platform, with steady-state and transient validations performed to verify model accuracy. Four PID control strategies were designed, including electric power deviation control (EPDC), coolant average temperature deviation control (CATDC), reactor power deviation control (RPDC) and three-channel control (TCC). Controller parameters were tuned using the trial-and-error method. For performance evaluation, three operating conditions were simulated, including 100%FP to 90%FP load step change, −100 pcm reactivity disturbance, and −0.5 kg/s coolant flow rate disturbance. For the first one, EPDC achieves the fastest parameter regulation with minimal settling time (26.43 s) due to its direct responsiveness to load changes. However, RPDC demonstrates superior performance for scenarios prioritizing rapid reactor power response (zero overshoot, 3.94 s settling time). Under reactivity and coolant flow rate disturbance, RPDC exhibits the smallest fluctuation amplitudes (159.2 W power variation under −100 pcm disturbance; 55.22 W variation under −0.5 kg/s flow rate disturbance) and fastest stabilization, attributed to its high sensitivity to primary loop parameter variations. This study systematically evaluates PID-based control strategies for Stirling cycle-based SNPS through comprehensive modeling and multi-scenario validation. The findings provide quantitative guidance for control strategy selection under different operational priorities, with EPDC recommended for load-following dominance and RPDC preferred for primary loop stability. The developed simulation framework and parameter tuning methodology offer valuable references for advancing control systems in next-generation space power applications.