Abstract: In the process of long-term operation of steam generators, although the secondary side of the water quality is strictly controlled, in the complex thermal hydraulic conditions, impurities will also accumulate in the steam generator. It mainly includes the deposition of the heat transfer tube and the blocking of the tube support plate. Among them, the deposition of impurities on the supporting plate will cause the blocking of the tube support plate. The blockage of the support plate may lead to local highspeed flow and cross flow in steam generators, which will cause flowinduced vibration and tube cracks in some situations. Therefore, it is necessary to study the deposition of the tube support plate. In order to predict the deposit distribution on the tube support plate of the steam generator, the impurity migration model and the tube support plate flow blockage model were added to the threedimensional thermohydraulic code of the steam generator STAF developed by NuTHeL of Xi’an Jiaotong University. The accuracy of the code, which was based on a porous medium method and the drift flux model, has been fairly well verified. The deposition on the tube support plate with and without ageing for 150 days were predicted in the paper. Then the influence of ageing was studied. First of all, the results show that there are more deposits in the upper part of the hot side of the tube support plate, which suggests that boiling is the main factor leading to deposition. Compared with the situation without ageing, the mass of deposits after ageing is reduced, and the difference of the deposition mass between the hot and cold sides is also significantly reduced. In addition, ageing also has a certain effect on the distribution of deposits. After ageing, the distribution of deposits is closer to the two sides of the tube support plate, which is similar to the distribution of flow velocity. The reason for this phenomenon is that flash evaporation is more likely to occur where the flow rate is high, making the soluble precipitate and thus exacerbating the ageing. The research of this paper can provide reference for the design and cleaning of steam generator in nuclear power plant. In practical applications, we can take some measures through the program prediction to reduce the harm caused by the tube support plate clogging. In the future work, we will continue to study the influence of tube support plate blockage.