In previous experiments the very complicated system or high-precision and large-range spectra-analysis apparatus was used to distinguish stimulated thermal scattering (STS) and stimulated Brillouin scattering (SBS) because the frequency shift of SBS is much larger than that of STS which is a few tens MHz generally, but the shift of SBS reaches several GHz typically. It will be difficult for common laboratorial conditions. Frequency responses of STS in Cu(NO3)2 colored acetone and SBS in pure acetone were investigated experimentally. It was showed that the linewidth of SBS fluctuated random and that of STS changed regularly as pump power increased. It can become a convenient and cheap approach to distinguish STS and SBS instead of high-precision and large-range spectrometer or complicated system. This method, as far as we know, has not been reported in references.