ACP100 (Linglong 1) SMR applied integrate reactor pressure vessel and once through steam generator, which has the advantages of compact structure and modular construction. A model including reactor core, primary circuit and secondary circuit of the ACP100 was built using APROS—Advanced PRO-cess Simulation Environment. Data collections are from ACP100 design manual. During the nodalization, some simplifications are made to ensure the simulation speed. The purpose of the model is to describe all the important parameters in detail and to achieve relatively high accuracy. The available process and I&C elements in APROS environment were used as well as the specified nodalization of the once-through steam generator. Submodels and important components are verified that the simulation results are within the allowable limits compared to the design data. The model includes 3D reactor core kinetics, reactor pressure vessel which is the primary cycle at the same time, pressurizer, reactor coolant pumps, once-through steam generators, main steam system, feedwater system, turbine, condenser etc. The regulation of pressurizer level and pressure, steam pressure, control rods and turbine load are also modelled. The model consists of 2750 thermal hydraulic nodes and 570 automation signals to achieve a through thermal hydraulic analysis of ACP100 SMR. Several simulations of the steady states at different power levels were performed. The simulation data including primary side temperature/flowrate, feedwater/steam flowrate, steam pressure/temperature etc. are compared to the result of design documents as well as other computer code. In that manner the model was verified and validated to ensure the reliable steady state results. Thus, the foundation is made for the further dynamic analysis of ACP100 SMR.