Aiming at the characteristics of multi-dimension and high sensitivity obtained by new single-photon linear APD devices, an algorithm based on single-photon linear APD is proposed to extract the distance information of weak echo signal. Firstly, the echo signal is modeled using the Poisson distribution property of the weak signal, followed by counting the number of echo photons per nanosecond, performing a sliding-window summation using a distance window of equal width to the pulse width. The position of the maximum value is used as the moment of reception of the signal pulse, which in turn back-calculates the distance information. In addition, the target search strategy before tracking and the range gate matching algorithm after stable tracking are designed to effectively reduce the background light interference and computational resource consumption. And the calculation accuracy rates of 100%, 99.93%, and 96.58% are obtained when the number of echo photons is 200, 10 and 5, respectively. The pulse accumulation algorithm is designed for the single photon signal, and the computational correctness of a single photon signal echo is 99.5%. Besides, the information extraction with a signal-to-noise ratio of 0 dB or even negative dB is realized through algorithm iteration for stationary targets, and the calculation accuracy of 0.03 photon signal echo detection is 96.1%. The simulation results show that the proposed algorithm can comprehensively apply the intensity information of single-photon linear APD and single-photon sensitivity to realize the distance information extraction under the limit sensitivity domain.