Abstract: There are plenty of screw fasteners which are loaded with complicated forces in reactor internals. To ensure the integrity of reactor internals, the stress and fatigue analysis of screw fasteners should meet the related requirements on ASME codes. The screw fasteners are very important to nuclear plant safe operation and affected by several kinds of static and dynamic forces under the operation conditions. According to the code requirements, the preload, force state, deformation calculation, loads category and combination, stress analysis and evaluation for screw fasteners are comprehensively researched. After the research achievements, a specific program on stress evaluation for screw fasteners was developed. The program makes the stress evaluation for screw fasteners more correct and effective, and provides reliable and convenient determination for engineering design and application.