The invention belongs to the industrial control field and in particular relates to a steel chimney corrosion monitoring system and method based on a non-contact ultrasonic technology. The system is composed of an electromagnetic ultrasonic probe, a climber, an annular guide rail, a longitudinal guide rail, a controller, a data acquisition instrument and a computer. The non-contact ultrasonic technology is utilized to measure the thickness of a steel chimney in a non-contact state, and the corrosion position and the corrosion risk of the chimney can be acquired through comparative analysis of thickness distribution of an inner steel barrel and thickness vibration tendency along with time history, so that an advice is given timely for maintenance. The system and the method can automatically, rapidly and precisely realize assessment and analysis of the steel chimney health condition, so as to reduce the corrosion risk and the corrosion degree of the steel chimney and improve the working efficiency of the steel chimney and even the whole production process.