The bag filter is a kind of important de-dusting equipment in the power, metallurgy, chemical and building materials industry. Its operation efficiency and running state are two technical indexes of great importance. As for detection of the two indexes, current existing detection methods have various defects. This paper mainly introduces a bag filter on-line monitoring system based on AC charge induction. By using the international advanced AC charge-coupling technology and digital signal processing technology, it can accurately monitor the bag breaking state of filter and put out alarm. In the bag filter on-line monitoring process, the system well solves the technique difficulties of the measuring equipment in such aspects as anti-blocking, wear resistance, low pressure losses, accuracy and reliability, etc. It has the advantages of high measuring accuracy and easy installation and maintenance, therefore, it can bring certain economic benefits and have the prospect of popularization and application.