Abstract: 48 X-ray flares observed by ISEE-3 satellite during May, 1980 to August, 1981 are analysed. It is found that one third of all are multi-bursts in six active regions. Relation of physical nature of these X-ray flares with corresponding sunspots area, type and magnetic structure of active region are studied. Some interesting results are obtained.1. Hard X-ray integral fluxes and spectral hardness at the peak of X-ray flares in the same active region and the sunspots area of the active region are positively correlated;2. The active region of mullt-bursts G-ray flares all have magnetic structure;3. The physical nature of X-ray flares in different active regions is not obiously correlated with the area of the active region.It seems that the gradient of the magnetic field in active regions, namely, the current of active regions, have a critical action during flare eruptions. In addition, the characters using the current loop model of solar flares are discussed.