A method to detect the impact energy using the fiber Bragg grating as the sensing element was presented. A simple impact system was built to detect the incident stress wave energy while fiber Bragg grating were axially symmetrically pasted to the round rod. The experiment result shows that both the amplitude of incident stress wave and energy transfer efficiency reach the biggest with two rod positive impacts. The energy of incident stress wave is mainly concentrated in the range of 0~5 000 Hz based on the analysis of signal in frequency domain. The energy transfer ratio of impact bar to round rod is more than 93% while comparing the incident stress wave energy and the kinetic energy of the impact bar, which meets the basic requirements of the testing for the impact mechanical properties.