Molecular spectrum lines can be viewed on the radio spectrum, but discrete digital power spectrum analysis algorithms would introduce errors that make it difficult to obtain accurate information about spectral lines. In this paper, the ratio correction method were studied and carried out to solve the problem of frequency offset. It is a kind of spectrum correction method, which is characterized by its simple, convenient and fast algorithms. The effect of such correction is determined by the change of the normalized frequency offset under two conditions: different spectral resolution with the same and different radio signals. Setting the radio frequency to be 80.0, 141.8 and 270.8 MHz, the frequency resolution were finally improved to 7.5 Hz/channel. By comparing the experimental results, the optimal frequency resolution of the sampling system used in experiment was 50.0 Hz/channel and 200 Hz/channel. © 2020 IEEE.