Abstract: The attitude displacement process of nuclear power large pieces has become one of the important factors for improving productivity and enhancing the workpiece's surface quality in processing and manufacturing,welding assembly,and non-destructive inspection.Therefore,the research of large and heavy-load upender is indispensable,but the best flip technology and analyzing of the upender's reliability for multifunctional overloading flip is rarely reported at home and abroad.Based on a nuclear large pieces upender,the research was carried out jointly with a heavy machinery factory.With the application of theoretical analysis,considering production efficiency and equipment safety factor,the best rotation angle of upender for different kinds of nuclear power large pieces was obtained.The research plays an important role in providing reference for making the best turning process of different kinds of nuclear power large pieces and ensuring the safety of equipment and operation efficiency.