In this paper, we apply the auto-focusing algorithm, which is based on the image sharpness evaluation function, to collinear double pulse laser-induced breakdown spectroscopy (DP-LIBS). Through the control software based on LabVIEW, the collinear DP-LIBS experiment system, CCD camera and three-dimensional mobile platform are effectively controlled. Image sharpness evaluation, the auto-focusing algorithm, and the three-dimensional mobile platform are combined to achieve sample auto-focusing function. The results show that the optimal interval between the two lasers is 0.55 μs. The stability of the atomic spectral line is higher than that of the ion line. The relative standard deviation of the spectral strength decreases from 16.7% to 6.7%. The quantitative analysis of the steel samples shows that the correlation coefficients of Cr and Mn measurements increase from 0.851 and 0.639 to 0.947 and 0.923, respectively. Overall, the auto-focusing system can improve signal stability and measurement accuracy.