In order to study the correlation between cloud droplet spectrum dispersion and cloud microphysical parameters, an observation technique based on short pulse modulated laser based on field programmable gate array, high resolution microscopic optical system, and coaxial digital holographic interferometry is proposed. The minimum size of cloud droplet detected by proposed technique is 2 μm, and the complete spectrum width data of cloud droplet can be obtained. Under different aerosol concentrations for three consecutive days in an expanding cloud chamber, the three-dimensional positions and diameters of cloud droplets during the generation and elimination process are observed, and the cloud microphysical parameters are calculated by using the observation results. Furthermore, the positive correlation between the dispersion of cloud droplet spectrum and cloud microphysical parameters in the process of generation and dissipation is analyzed. By comparing the dispersion distribution of cloud droplet spectrum under different aerosol number concentrations, it is concluded that with the increase of cloud droplet concentration, the value range of the dispersion will gradually decrease, and the dispersion will decrease relative to the fitting line.