We study the two-ribbon solar flare on 7 October 1979. As may be seen from the GOES soft X-ray data, the preheating phase preceded the flare impulsive phase. The semiempirical photospheric models for different stages of flare development are calculated on the basis of observed Fraunhofer spectra. The modelling results reveal inhomogeneities of temperature, gas pressure, and other parameters. Disturbances of the matter below undisturbed photosphere base prevailed during the preheating phase. Narrow and cool layers were displaced upwards in the 0.5 min time interval. During the impulsive phase and at the flare maximum the upper and middle photospheric layers were mainly disturbed. This period is characterized by the downward displacement of the lower boundary of wide low-temperature region in the upper photosphere. The photosphere perturbations were still preserved during 25—30 minutes after the flare maximum. The turbulent motions were inhibited throughout the flare.