Abstract: The vermicular graphite rate is one of the main parameters in measuring the quality of vermicular iron, which requires a precise, rapid measurement and control in production. The relationship between the ultrasonic velocity and the vermicular graphite rate in vermicular iron was described, the ultrasonic velocity in vermicular iron was measured by thickness independent reflector plate(TIRP) and the software was compiled using VC6.0, The system realized vermicular iron blast furnace-based automatic detection and adjustment, greatly reduced the difficulties of controlling the rate of vermicular graphite cast iron, decreased testing and adjustment time.