Abstract: One of the greatest drawbacks of range-gated laser active imaging system lies in the plight that the two-dimensional slice could not provide complete spatial information on some remote objects. Aiming at this problem, a three-dimensional reconstruction method that combines the threshold method to cut off the measured gray-scale curve and cross-correlation method to draw range information and could provide relatively high precision was proposed. In the paper, threshold method was firstly utilized to remove the zero points from the measured gray-scale curve to mitigate the following effect on the distance computation that adopts cross-correlation method. Correlate the interceptive measured gray-scale curve of every pixel and the ideal gray-scale curve, the distance of each pixel with the time delay corresponding to the peak value could be deduced and the three-dimensional coordinates of each pixel with the combination of the system parameters were computed. Finally, the three-dimensional reconstruction of the arbor from 1.2 km could be obtained with the procession of the slices.