This paper presents the experimental study of instantaneous strain-type granitic rockbursts. It uses the nondestructive acoustic emission (AE) testing method to monitor the rock internal damage during the simulation test. Using real-time waveform signals, we can plot the evolution of stresses and voltage signals in full time-domain. Combining with the cumulative AE energy curve, we can determine five key points which are the first inflection point A (positioned at initial load), the two turning points B and C (located at obvious rise ledges), the dramatic increasing point D and the final peak point E. The five points can be extracted and processed with the Fast Fourier Transform (FFT) in Matlab commercial software. The results indicate that the dominant frequency component of the granitic rock sample is 106 kHz at the initial loading stage. As the load increases, the frequency changes from low value to high value, the band of frequency becomes wider and wider, and the shape of wave changes from unimodal to multimodal. These frequency changes indicate the complicated frequency components and various fracture modes. At the time of rockburst occurring, the band of frequency becomes narrower and the shape of wave changes back to unimodal. The dominant frequency decreases to 106 kHz and equals to the initial value, which indicates a large amount of energy is released.