To explore the operational characteristics of the sodium-cooled fast reactor (SFR) integrated with the Stirling power conversion device system (SFR-SPC), a transient calculation module for Stirling was incorporated into the self-developed SFR system analysis program, FR-Sdaso (Fast Reactor State Design and Analysis Software), enabling the system program to perform transient simulations of the main process system from the reactor core to the Stirling engine. The Stirling module was validated by comparing publicly available experimental data with program calculation data. The validation outcomes indicate that the calculation results of the program are in excellent alignment with the experimental data, demonstrating the accuracy of the program. Subsequently, a system model of a small SFR coupled with a Stirling power conversion device was established using FR-Sdaso. The effects of variations in four parameters, namely power, coolant flow rate, cooling water flow rate, and Stirling operating pressure, on the coupled operation of the system were analyzed. The results demonstrate that for the SFR-SPC with small sodium load, the disturbance can be transmitted to the whole nuclear power system in a short time, and Stirling engine can alleviate the external disturbance to a certain extent. And the Stirling engine is so responsive to pressure variations that should be controlled as a crucial parameter. This study preliminarily explored the operational characteristics of the SFR coupled with the Stirling system, performing sensitivity analysis on parameters like power, flow rate, and operating pressure. The research results can serve as a reference for the conceptual design of new nuclear power systems.