We present a technique for observing solar sub-terahertz flares (STFs) with the RATAN-600 radio telescope. STF observations are proposed to be carried out during the routine multi-azimuth observations of the Sun with a reduced aperture at a frequency of 93 GHz. The expected beam patterns of the antenna system at frequencies of 30, 93, and 140 GHz (10, 3, and 2 mm) were calculated taking into account possible errors of the element surfaces, errors in their mutual alignment, as well as the primary feed placed off-focus. Two-dimensional convolutions between the beam patterns and the solar disk model were obtained, one-dimensional scans of which correspond to the expected radio images of the Sun from RATAN-600.       The expected STFs were assessed with respect to the model according to which sub-terahertz emission is generated due to the thermal bremsstrahlung mechanism of optically thick plasma in the chromosphere and the transition region of the Sun.       We propose simultaneous STF observations with RATAN-600 in a frequency range of 1–100 GHz and the Bauman Moscow State Technical University RT-7.5 radio telescope at frequencies of 93 and 140 GHz. Such cooperative multifrequency observations will make it possible to clarify the W-shaped spectrum of STFs in the decimeter, centimeter, and millimeter wavelength ranges and to elucidate the nature of sub-terahertz emission from solar flares with a positive spectral slope.