Аннотация:Modelling of the gas-dynamic process in giant coronal arches for interpretation of the large prolonged X-ray flare on subgiant UX Ari with less than solar gravity is carried out. The case where plasma is heated near the top of the giant loop is considered taking into account the thermal conduction and radiative losses. The observational duration of the soft X-ray flare radiation and peculiar features of the temporal behaviour of the temperature can be explained if this process is developed under prolonged heating in giant loops with densities more than 10**11 cm-3. The model of the X-ray flare source agreeing with the observed value of the emission measure, includes around 8 loops lifting up to heights around 10**11 cm, i.e. more than 0.2 Rsun. It is proposed than the energy of such non-stationary phenomena is supplied from the large-scale (global) magnetic fields, and these flares are not a result of evolution of local magnetic fields as happens during impulsive stellar flares.