Abstract: The tank level measurement is an important daily service in refineries, tank farms and fuelling stations. The ultrasonic level measurement technology is a new technique developed in recent years, which is used to measure tank level and has a wide applicability, a high reliability and a sound performance/price ratio, but its shortcoming is low accuracy. Improving measurement way and reducing secondary instrument's errors can increase the accuracy of this technology. At the same time, the more work also to do for applying this technology to the tank level measurement are raising the intellectulization level for the ultrasonic measurement system, making a further study on the ultrasonic propagation mechanism for petroleum product, determining the relationships of ultrasonic propagation velocity with petroleum product density temperature, pressure and petroleum product characteristics as well as establishing a practical corrective equation.