Based on the application of range-gated technology in the airborne laser detection imaging system, temporal relations of the parameters in the model of range gating are analyzed in detail and effective scope of atmospheric backscatter and the before- and after- pulse points of the unit section are obtained. A horizontal range-gated imaging model is established and the calculation method of back-scattering light intensity is given, and then tilt detection distance of airborne laser active imaging is revised. Based on the object-image relation of points on the scattering section, the light path diagram of detecting imaging system is built and the corresponding relationship of light intensity between scattering points and receiving points is provided. The variation regularity and distribution of light intensity on the detector under horizontal and tilt detection are gained. An outfield test platform is set up, and the relative error between measured data and simulation results is controlled within five percent, the measured data are consistent with the simulation results to a higher degree, which demonstrates the effectiveness of the built model.