In order to explore a new real-time demodulation method of impact energy for fiber Bragg grating(FBG) sensor, the impact energy of sheet metal is measured by FBG edge filtering method. For the impact process of low quality sphere acting on aluminium plate, the right edge moving filter demodulation method of FBG spectrum is used in the experiment. For the impact process of high quality sphere acting on acrylic(PMMA) and aluminium plate, a new demodulation method based on damping attenuation principle is proposed. The experiment results show that the peak value can be directly used as the demodulation basis for a weak impact energy signal, and its goodness of fit is 0.988, sensitivity is 0.0007476 v/g. For a stronger impact energy, the linear fitness of PMMA plate and aluminium plate is 0.94 and 0.89 respectively when using the time length corresponding to the peak attenuation of 10% as the demodulation.