A beam expanding focusing lens of single scanning laser vibrometer is analyzed and designed by ZEMAX. Firstly, the Gauss He-Ne laser source is simulated, and then the initial structure of the system is calculated. The relationship between the moving distance of the front lens and the laser focusing distance is analyzed, and the spot sizes at different focusing distances are obtained. Finally, the mechanical structure of the adjustable focusing system is designed. The adjustment of the structure is smooth, and the front lens can not rotate. Thereby the errors caused by rotating lens are reduced.