Abstract: The hydraulic and thermal coupling calculation for ship steam systems is the theoretical basis for system optimization and pipeline layout design. As the arrangement of steam pipe network can be quite complex, and it could include multiple pipeline fittings, a hydraulic and thermal coupling calculation model, under the city heating condition, is established in this paper by considering vapor compressor, characteristics of heat transfer, friction of network. The calculation model is then solved with the fourth-order Runge-Kutta scheme. The three performance states of the onboard steam system are calculated, and the results agree well with experimental data with a deviation less than 4.1%. In brief, the proposed method can be applied in the calculation and analysis of the steam pipe network of ships.