Abstract: At present, the research on compressed sensing mainly focuses on reducing the reconstruction error and the reconstruction time by improving the reconstruction algorithm. The reconstruction error and reconstruction time lie in the practically allowed range. Researchers usually pay less attention to improving techniques of spectral resolution in the frequency domain analysis. In this paper, we use the modulated wideband converter (MWC) to sample the sparse signals, and employ the orthogonal matching pursuit (OMP) algorithm to reconstruct the input signals. By extending the sampling time, low sampling rate in one channel is realized, and the spectral resolution is improved. The experimental results of low-frequency radio astronomical signals show that the spectral resolution increases from 0.435 7MHz to 0.200 2MHz when the number of samples in time domain increases from 459 to 999 with the same sampling rate for all channels. Meanwhile, the total sample number of the system increases from 102 to 222. Our work provides a good reference for processing the narrowband high-frequency signal, such as radio astronomical signals.