The chain transmission system of heavy-duty upender is critical for turning body safe operation and parking,therefore,the reliability analysis of the chain transmission system is indispensable for the research and development of large heavy-load upender.Based on a nuclear large pieces upender which we jointly developed with a heavy machinery factory,the complex force state in the equipment operation process is analyzed.With the application of theoretical analysis and motion simulation method,the dynamic change trend of the chain transmission torque when carrying extreme load in the different flip solutions is got,the biggest stress field of the chain drive system is analyzed with the finite element software ABAQUS.The cost of research and development of the equipment is reduced,the design cycle is shorten,the reliability of equipment operation is improved,which has a certain reference value for the dynamics research of chain drive system in large and heavy equipment mechanics.