In this paper the evolution of force-free magnetic field was discussed.The kine-matical implication about the time variation of force-free factor and detailed processes of energy storage were analyzed.The limitation was pointed out when storape processes in solar flares were determined by the static force-free field theory.Therefore,a process of energy storage which is maintained by meridianal flow is suggested.Combining those processes of energy storage with some explosion processes triggered by a suitable instability,the main features of solar flares may be explained further