The invention relates to the field of in-air device insulating internal discharge detection and specifically relates to a frequency selection method of a receiving frequency of an in-air device insulating internal discharge detection system. The method includes the following steps: acquiring time domain signals in a full-frequency-band manner; carrying out Fourier analysis on the time domain signals according to frequency bands so as to obtain frequency domain signals; dividing a 30-1800 MHz frequency band into four frequency bands: 30-100MHz, 100-300MHz, 300-900MHz and 900-1800MHz frequency bands so as to judge the amplitudes of interference signals of the frequency bands and then obtaining a frequency band with the minimum amplitude of interference signals and if the amplitudes of interference signals of two frequency bands are identical, selecting a frequency band with a higher frequency as a frequency band with the minimum amplitude of interference signals; and selecting a frequency point with a highest signal to noise ratio from the frequency band with the minimum amplitude of interference signals as a receiving frequency of discharge signals. The method adopts a method of firstly screening an appropriate frequency band and then screening an appropriate receiving frequency point from the screened frequency band to receive discharge signals to eliminate frequency bands which are not suitable for receiving the discharge signals so that clearest discharge signals can be obtained and the positioning precision of the discharge signals are enabled to become higher.