Abstract: For main coolant piping 90° elbow of CPR1000 nuclear power station, the theoretical thickness distribution was researched, and an optimized elbow structure was designed. The main difference between the optimized elbow and present design elbow is as follows: for the present design 90° elbow, the 120° of internal rounding area are thickened, then transitioned to the mid surface, while the external rounding area keeps normal thickness; for the optimized structure, based on the departure of internal and external circle center of elbow section, wall thickness is designed with regularly changing from higher thickness in the internal rounding area to less thickness in the external rounding area, and keep the internal section a regular circle. This optimized elbow structure can realize mechanization, and improve efficiency and machining precision.