In this work, the process of forming micro-droplets due to instability and fragmentation after short chain alcohol solution spreads on the surface of oil layers is studied. Based on the free energy theory of the liquid-liquid interface, the relationship between the binary mixtures spreading on the surface of the liquid layer is derived, and the concentration range of short chain alcohol solution spreading as a thin film on the surface of the oil layer is calculated from the Hiskovsky formula. The Malangoni flow caused by the difference in evaporation rate between the center and edge of the droplet film perturbs the boundary of the liquid film, causing finger-shaped liquid columns to grow at the edge when the droplet spreads to its maximum. In this work, the expression for the critical wavelength and maximum wavelength of boundary instability are derived based on the perturbation model, and the reason for finger shaped liquid column fragmentation is explained based on the Plateau Rayleigh instability. A concentric cylindrical shell liquid column model is established to simplify the calculation and predict the location range of “droplet explosion” of droplets with different viscosity ratios on the liquid layer. Through theoretical calculations and experimental verification, it is found that the alcohol solution fragmented into small droplets within a length range of 4.51–5.98 times the width of the liquid column. This study provides theoretical guidance for existing application fields such as film forming technology and coating technology. The hypotheses, assumptions, and simplified models preliminarily verified experimentally provide solutions for some technical difficulties in the research fields of micro reactions and nanoparticle preparation in chemical industry.