Oxygen is an essential substance for sustaining life. Reliable and stable oxygen supply is indispensable for medical emergency treatment, industrial production, and daily health management. Within the supply chain of oxygen equipment, direct selling manufacturers act as a bridge linking technology and market demands. By shortening distribution channels and optimizing production workflows, they deliver cost effective oxygen solutions to the market. This article provides an in depth look at core knowledge in this sector from three dimensions: technical principles, industrial chain division of labour, and selection criteria.