DCBM10A voltage buffer device provides continuous power within the stipulated time for subsequent load, it’s very important to accurately calculate discharge time. First, through theoretical deduction the capacitor discharge state equation is established. Then SVD singular value decomposition theory is introduced and the theory is used to analyze the equation, and discharge time is determined. And then Marr wavelet and wavelet transform modulus maximum theory are selected respectively to process buffer signal. The two results are analyzed and compared, which embodies SVD theory superiority. Finally experimental platform is built, which demonstrates the effectiveness of this method. This work is supported by National High-tech R & D Program of China (863 Program) (No. 2015AA050101).