Based on the working principle of pulsed laser ranging, the general equation of the light echo power of laser ranging for the flight targets is derived. Based on the pointing error theory of the target detection and tracking system and the ranging equation, a computation model of the detection probability for the range system is established. The influences of the laser divergence angle, the system tracking precision, the target scale, the detection distance and the system receiving aperture on the light echo stability of pulsed laser ranging are simulated and analyzed by the Matlab simulation software. A system of pulsed laser ranging for the flight targets is designed, the system parameters are determined according to the theoretical analysis results, and the experimental platform is built. The detection performance of this system is confirmed by the tracking and ranging experiment for the unmanned aerial vehicles. The effectiveness of this model is verified by the comparison between the detection probability and the theoretical derivation one for the target boards with different sizes.