Because of the GPS signal transmission channel exists on a large number of nonlinear and non-stationary multiplicative noise, interference on GPS signals. The traditional method of GPS signals to eliminate multiplicative noise denoising effect can"t meet the requirements, to establish the coordinate system of precision is reduced, reduces the accuracy of measurement of road roughness. For this, put forward a kind of based on the GPS under the multiplicative noise optimization of road roughness measurement method. Will receive GPS signals using the discrete wavelet transform method to eliminate the multiplicative noise, get accurate data. Use of 3 d space coordinate system GPS road roughness measurement model is established. Experiments show that this method can eliminate the multiplicative noise of GPS signals, and accurate measurement of road roughness.