The purpose of the present invention is to disclose a system and method for converting a PDS three-dimensional model into a RELAP5 model. Compared with the prior art, the PDS three-dimensional model can be automatically converted into an XML file supported by RELAP5 software, and the conversion of the layout model to the mechanical analysis model is realized. Automatic conversion avoids labor waste caused by secondary modeling, greatly improving design efficiency and quality; supports four generation modes with system as the unit, custom pipeline as the unit, model as the unit and mechanical analysis package as the unit, flexible Easy to use, the whole process is fully automatic, without human intervention, easy to operate, high efficiency, greatly improving the utilization rate of the PDS 3D model, supporting equipment mapping and removing pipeline functions, supporting removing tap point follow-up connections and removing small pipe functions, It is applicable to various application scenarios, supports threshold setting, improves the fault tolerance rate in the modeling process of the three-dimensional model, and realizes the object of the present invention.