Abstract: As the pressure and heat transfer boundaries between primary and secondary sides, the steam generator (SG) should be integrated during operation. However, SG suffers from the problems including vibration, wear, fatigue and corrosion, which will lead to the degradation of tubes and other components and may lead to the failure of SG. The research on the degradation of SG is associated with many disciplines, including thermohydraulics, structural mechanics, water chemistry and materials science, among these, the thermohydraulics are the foundation of other analysis. In the current work, SGTHPorous3D, a 3D steam generator thermohydraulics analysis code based on twofluid porous media model, was developed for the prediction of 3D thermohydraulics in the Utube SG (UTSG) and helical coiled SG (HCSG). First, the twofluid porous media model for the straight tube, U-bend and helical tube bundle was proposed for the general application of UTSG and HCSG. A velocity projection method was employed to estimate the flow resistance and heat transfer for inclined sweeping flow over different types of tubes. With these models, the 3D numerical strategy based on coarse mesh was developed for the shell side of SG. Second, as for the tube side flow, the parallel 3D multichannel model was used to simplify the numerous spatially distributed tubes. The effects of centrifugal force were considered by employing the flow resistance and heat transfer maps specially developed for Ubend and helical shaped tubes. Finally, a data mapping method was also developed for the tubetoshell side heat transfer between cells of different spatial scales. A partial relaxation scheme was used to accelerate the convergence of coupled heat transfer, where the heat flux was relaxed while the temperature wasn’t. The experiment data from the Westinghouse MB2 UTSG, the KAERI HCSG and the SJTUNETH HCSG were used for code validation. The SGTHPorous3D code was applied to predict the 3D thermalhydraulics parameters in the CAP1400 SG. The distributions of thermal-hydraulics parameters for each phase and the mixture phase were obtained. High non-uniformity can be observed for the flow and heat transfer parameters. The ratio between heat released in the hot side and cold side is as large as 2.7. The crossflow energy related to the flowinduced vibration is also derived to find the possible location of tube damage. The most probable location for a potential tube rupture locates at approximate 0.4 rad in the hot side. The results show that the SGTHPorous3D can predict the 3D thermalhydraulics parameters in both of the tube and shell sides of UTSG and HCSG, which provides support for the heat transfer design and flowinduced vibration analysis for the SGs.