In order to lead the laser beam transmit in the atmosphere convergently, an experiment of laser focus at a distance of 450 m and 300 m has been operated in outdoor place. The actual manipulations are as follows: Firstly, the laser is collimated by a beam expander, then the near-parallel laser beam transmits through a Galileo telescope system, and the distance between the concave lens and the convex lens can be tuned through a precise displacement platform, so the focus of the system can change due to the tiny displacement of the concave lens. Secondly, the average power of the laser spot can be measured using power meter, and the power is 47.67 mW and the standard deviation is 0.67 mW while the focal length is 450 m. Thirdly, the energy distribution is found through a laser beam analyzer. The spot images are saved by using the beam analyzer, then the saved image can be processed with Matlab software afterwards. The functions named EDGE and Sobel operator are used in the pre-processing of saving image, then method of median filter is used in the course of image de-noising and 53H filter is adopted in the signal analysis. The diameter of laser spot is obtained by the methods above, and the diameter is 5.56 mm and the standard deviation is 0.24 mm. The spot center excursion is 0.56 mm, and it is 10.43% of the total diameter of the laser spot. At last, the key factors of the energy dissipation in the focusing system can be summarized as follows: restriction of the diffraction limit, attenuation in the atmosphere, and geometrical aberration of optical system. The diffraction limit and the geometrical aberration are significant in the three factors above, so we can reduce the impact of the both factors during the design of optical system. The reliable referenced data of the design of the system can be acquired through the primary experimental research.