The laser ranging echo signals often contain impulsive noises, and have low signal-to-noise ratio, which make the traditional laser ranging algorithm performance decline, even if useless. This paper addresses a robust time delay estimation algorithm to laser modulation signal ranging. Signals with noises are modeled by using Alpha stable distribution. First, impulsive noises are suppressed and signal-to-noise ratio is improved by fractional lower-order convariance function. Then, the time delay information between echo signals and transmitting signals is obtained by using correlation function, so as to obtain the information of distance. Theoretical analysis and computer simulation results show that, the algorithm can be used for both echo signal containing Gaussian noises and impulsive noises. It has wide range of application and good practical value.