Abstract: Beam collimation mechanism of the fast axis collimation (FAC) microlens is described, and theoretical accuracy requirements for adjusting advice and the selection of lens are analyzed, for the output beam of diode laser vertical stack to achieve small divergence angle and high pointing accuracy. The images of diode laser bar in the near field and far field are realtime monitored through optical imaging methods to realize coarse and fine adjustments of FAC lens, respectively. The output power of the 20 bar vertical stack is 2 kW, and the far field divergence angle of fast axis collimated beams is 4.4 mrad, with the pointing accuracy among bars of less than ±1.7 mrad. The monitering precision and the collimation influencing factors are analyzed, and the key of optimization is pointed out