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Single-photon detectors possess the ultra-high sensitivity,but they cannot directly respond to signal intensity.Conventional methods adopt sampling gates with fixed width and count the triggered number of sampling gates,which is capable of obtaining photon counting probability to estimate the echo signal intensity.In this paper,we not only count the number of triggered sampling gates,but also record the triggered time position of photon counting pulses.The photon counting probability density distribution is obtained through the statistics of a series of the triggered time positions.Then Minimum Variance Unbiased Estimation (MVUE) method is used to estimate the echo signal intensity.Compared with conventional methods,this method can improve the estimation accuracy of echo signal intensity due to the acquisition of more detected information.Finally,a proof-of-principle laboratory system is established.The estimation accuracy of echo signal intensity is discussed and a high accuracy intensity image is acquired under low-light level environments.