For dealing with the problem of being unable to sample beat signals with equal interval that is inherent in the Pseudo random Noise (PN) code modulated Doppler laser radar, a new Discrete Fourier Transform (DFT) method which applies to non-uniform sampling data was proposed. Firstly, system model of Doppler laser radar for simultaneously measuring range and speed was provided, and the reason of being unable to sample beat signals with equal interval was pointed out. Then, by theoretical deducing, a new spectrum analysis method was proposed for processing non-uniform sampling signals. Finally, simulations were performed to verify the feasibility of applying the proposed method to non-uniform sampling data. As a result, within Doppler frequency range which is created by moving targets in roads, the method can obtain the frequency of non-uniform sampling Doppler signals efficiently even when Signal-to-Noise Ratio (SNR) is low to 0 dB.