The extended pseudo-random encoding can solve the problem of the fuzzy distance, which is brought by high repetition frequency laser ranging in long target distance. But the extended pseudo-random coding methods are diverse. The effects of different amplitude encoding modes on the ranging accuracy are studied under different laser source repetition frequencies, and the Matlab simulation is carried out. The theory and simulation results show that the probability of "1" in optimal coding trends from 1 to nearly 1/2 with the increase of repetition frequency. When the probability is 1/2, the randomness is the best and the detection efficiency is high. The peak value is still obvious in weak noise environment. Therefore, in the practical application of distance measurement, choosing the appropriate coding method according to different repetition frequencies can optimize the ranging algorithm and improve the ranging efficiency.