ASME BPVC Section III will enhance the application value of its codes and standards as one of its development directions. In fact, there are many areas for improvement in the guidance of ASME codes and standards for the manufacturing of nuclear power equipment. In the design and manufacturing process of the steam generator in CAP1400 nuclear power plant, there is no systematic guidance method for the process evaluation of tube-to-tubesheet hydraulic expansion in the codes and standards. This paper analyzes and explains the draft code case submitted to the committee by the ASME BPVC III China International Working Group on this technology point, demonstrating the necessity and value of this draft code case. This draft code case will supplement and improve the performance requirements and assessment criteria for the expansion process evaluation of hydraulic expansion joints for steam generator tube-to-tubesheet in the ASME nuclear codes and standards. This draft code case will assess the structural integrity of the tube-to-tubesheet joint, evaluate the rationality of the strength expansion process and parameters, and also establish rules for evaluating the mechanical performance of the strength expansion joint. These will guide the production practice of steam generators and play an important role in improving product reliability. This paper also provides the scope of application, effectiveness, determination of tube expansion pressure, evaluation and acceptance requirements, and data organization of hydraulic expansion process evaluation cases, and provides basic explanations if necessary. Through the research, this draft code case will receive more support, and it is hoped that it can pass the ASME committee's review as soon as possible, guiding more equipment factories to improve the process level of steam generator manufacturing.