Abstract: Currently, all standards and manuals of petroleum industry in China provide little regulations on the instrument air system in pump stations and gas compressor stations. In order to specify the equipment selection and design of such system, and combined with relevant standards and engineering experience of instrument air in China and abroad, this paper presents the main composition and basic approaches of equipment selection of the instrument air system in the stations. The calculation formulas of the blast capacity of instrument air system and dry air tank volume based on the gas state equation are derived which indicate the key quality indexes of instrument air. It provides a basic way for the equipment selection and design of instrument air system in the stations.