Abstract: In the transforming engineering of Huangdao underground oil storage, radar level gauge monitoring systems are installed on 1# and 3# underground oil tanks individually. The system can send an emission wave f0 through antenna while reaching medium level, detect frequency change Af between emission wave fo and f1, and the relationship in proportion to detected level distance d (d = Δf×41.7 Hz/m), so as to calculate the level of the medium inside tank accurately and send such major data as level, temperature and seepage level up to ground control center for monitoring. It will reduce labor intensity and raise support factors of safety operation. The system has the characteristics of high accuracy, quick transfer speed, good explosion-proof property and convenient repair, etc. The article introduces the structure principle of the system and technical characteristics.