The synthetic ammonia industry, as one of the important pillars of the modern chemical industry, occupies an important position in the national economy. The process of synthesizing ammonia, the water gas shift reaction is a crucial step, aiming to convert carbon monoxide in the raw gas with steam into hydrogen and carbon dioxide, increasing the hydrogen content to meet the demand for subsequent ammonia synthesis. The shift catalyst plays a key role in the process, as it can reduce the activation energy of the reaction, the reaction to proceed at a significant rate under relatively mild conditions, greatly improving the production efficiency.  An overview of the modern shift catalysts, the types and reaction mechanisms were provided and the types of modern synthetic ammonia processes and the selection principles, optimization, etc. of shift catalysts were summarized.