The Moon has a large size,which can effectively block the low-frequency electromagnetic interference from the Earth,so the lunar far-side is the best place for low-frequency radio astronomical observation. In this paper,the significance of using a very low frequency radio spectrometer(VLFRS)for the low frequency radio astronomical observation on the back of the moon is discussed. And the goals,as well as the basic principles,design,composition and achievements of the VLFRS are described. Finally,experiments on the radiation spectrum of low frequency electromagnetic wave in Zhongguancun area,Beijing are analyzed. The results show that the low frequency radio signals in the 0.1~40 MHz band, which are emitted by the radio stations and the time-service centers, can be clearly detected by the VLFRS.