The Brillouin distributed optical fiber sensing technology can measure the optical fiber strain, but the measurement precision is affected by noise easily. So a new method of wavelet denoising is developed to enhance the measurement precision of optical fiber strain. The new method not only takes the wavelet transform detail coefficients to threshold quantification, but also removes the noise from the approximation coefficients. So the new method can also obtain high precision Brillouin spectrum with fewer decomposition scales as the signal-to-noise ratio (SNR) of Brillouin spectrum is low. The research results show that the method can reduce the Brillouin spectral noise effectively. Compared with the conventional wavelet denoising method, the new method can decrease the wavelet transform calculation and the denoising effect is better, so the optical fiber strain measurement is more accurate.