Abstract: In this paper, the observational data of hard X-ray emission of solar proton and non-proton flares proveded by SMMsatellite during 21st solar cycle are analyzed. The results show that for proton flares the correlativities among the hard X-ray parameters, such as peak. flux, integral flux, ratio of peak flux to the increasing time, maximum X-ray photon energy and duration time, are very notable, shile they are ambiguous for non-proton flares. Based on the different behaviours between proton and non-proton flares, as a testing it is tried to warn solar proton events (1980.2-1986.2) by using the method of the fuzzy clustering analysis. The testing results show that this new method is very feasible. Accurate warning rate is 88.5%, false warning rate is 53.1%.