A measurement and verification method based on Michelson interferometers is proposed for investigating the influence of medium parameters on the temporal coherence of stimulated Brillouin scattering (SBS). The physical mechanism behind the influence of temperature on the temporal coherence of SBS is presented theoretically, and the influence of water temperature on the temporal coherence of SBS is measured and analyzed experimentally. The research results indicate that the temporal coherence of SBS is directly related to water temperature. As the temperature decreases, the temporal coherence of SBS deteriorates. When the temperature is fixed but the optical path difference of coherent light increases to a certain value, the corresponding coherent pulse waveform of SBS is no longer quasi-Gaussian.