Abstract: With the Kuperus-Raadu model to describe the interaction between a prominence bud the background magnetic field, and Lundquist field to describe the distribution of current and magnetic field inside the prominence, the observational data of eruptive prominence on August 18, 1980 is systametically analysed and the physical nature in its eruptive process is discussed. The results show:(1)the physical cause of prominence to erupt is the kink-instabity of Lundquist field;(2)in the eruptive process, the magnetic energy of prominence releases fast so that the current intensity decreases continuously and prominence goes up and approaches stable state gradually;(3)the eruption of prominence may be one of the most important factorcausing CMEs.