For improving the measurement precision of the gain coefficient of semiconductor optical amplifier (SOA) and avoiding the influence of the optical spectrum analyzer′s resolution and noise, a Hakki-Paoli (HP) method combined with the wavelet denoise and deconvolution (HP-DD) process was presented. The HP-DD principle including deconvolution algorithm and wavelet denoise was analyzed. Based on the simulated amplified spontaneous emission (ASE) spectrum and measured ASE spectrum, wavelet denoise and deconvolution process were demonstrated to improve the precision of the measurement and the noise tolerance.