Based on the status quo of modularization of equipment design, the evolution of equipment structure and the order of importance ranking by using importance theory were analyzed. On the basis of the gradual evolution from single component to five-component structure and N-component series-parallel structure, the evolution law was sorted out, and the importance analysis of the typical structure was carried out. The evolution of equipment structure and the order of importance of each component are obtained, which fills in the blank of the research on the importance drift law of the equipment, and provides technical support for the reliability optimization design of the equipment.