Abstract: An analysis of the properties of soft and hard X-ray flux distribution in solar flares observed by GOESand SMMsatellites shows that there are two distinct kinds of solar flare, i.e. the prominent thermal and non-thermal events. The main characteristics for these two kinds of event are: (1) the prominent thermal event is consisted of gradual type flares, while the prominent non-thermal event is impulsive ones; (2) the energy spectrum of hard X-ray is relatively "soft" for the prominent thermal event and "hard" for the non-thermal event; (3) the releasing rate of non-thermal energy for the prominent non-thermal event is 3-10 times larger than that for the thermal events; (4) for the prominent thermal event it seems that the slower is the evolution of flares, the larger is the peak flux of soft X-rays; (5) the prominent thermal and non-thermal events constitute respectively 40% and 60% of the solar flares. Finally, the possible mechanism responsible for the prominent thermal and non-thermal events is discussed.