Combustion control is the most important aspect in boiler unit operation, while the boiler air flow monitoring is the main content of combustion monitoring. Therefore, real-time and accurate online monitoring of the air flow in boiler main and branch pipes is of great importance for the economy, safety and environmental protection of the boiler combustion. This paper mainly introduces an air flow on-line monitoring system in utility boiler based on AC induction. By using the international advanced AC charge-coupling technology and digital signal processing technology, it overcomes the present technique difficulties of air flow on-line monitoring system. It has the advantages of high measuring accuracy and easy installation and maintenance. Also, it is applicable to the air flow on-line monitoring in different types of air ducts, therefore, it can bring certain economic benefits and have the prospect of popularization and application.