Abstract: To enhance mission safety and cost-effectiveness, this study addresses the challenge of reliability assessment for reusable rocket engines across multiple mission phases. Key operational stages—ignition and launch, maximum dynamic pressure, stage separation, secondary orbit insertion, and landing capture—are analyzed using the GO-FLOW methodology to construct a comprehensive system reliability model. Physical components are abstracted into operators, with signal transmission mechanisms employed to evaluate the dynamic evolution of propellant supply, combustion, and control subsystems across these phases. A performance consistency metric is proposed, with calculations demonstrating a system-wide performance consistency of 80.6%, indicative of high reliability. Sensitivity analysis, performed using MATLAB, involved adjusting the key operator parameter from 0.95 to 1.00. The results identified the nozzle as the most influential component, contributing up to 14.9% to system performance consistency, followed by the propellant tank (11.7%), fuel pipeline (8.1%), control valve (7.1%), and combustion chamber (14.6%). These findings provide a quantitative foundation for pinpointing critical vulnerabilities in the system. Key components impacting reliability at the five mission phases include igniters, control valves, combustion chambers, gimbal mechanisms, and turbopumps. Compared to conventional reliability analysis methods, the GO-FLOW approach demonstrates superior dynamic modeling capabilities and computational efficiency. This study offers novel insights for the design and operational planning of reusable rocket engines, advancing their reliability and performance in multi-phase missions.