The rays emitted by nuclear radiation (such as gamma rays, etc.) have strong penetrating ability. And through the medium of different thickness has different attenuation characteristics. The nuclear radiation level meter uses this principle to measure the liquid level. The nuclear radiation source of the nuclear radiation level gauge is installed outside the oil tank with a point or narrow structure. The elongated nuclear radiation source detection element is also installed outside the oil tank. It can realize the detection of dynamic change of liquid level. In addition to measuring with nuclear radiation rays, neutron rays can also be used to measure liquid level. The ray level meter is very convenient to install and has high measurement accuracy. Because it does not have any parts in direct contact with the measured object. It is especially suitable for measurement problems that cannot be solved by traditional measuring instruments.