Emulsion stability is a key parameter for oil-based and synthetic-based drilling fluids. To deeply investigate its stability mechanism and optimize formulations, this study utilized the multiple light scattering method to systematically examine the effects of emulsifier type, organoclay concentration, emulsifier concentration, calcium chloride concentration, and oil-to-water ratio on the dynamic stability of a biomass-based synthetic drilling fluid, LAE-12. By combining multiple light scattering with electrical stability (ES) tests, the influence of each factor on emulsion stability was determined. The results show that the emulsifier SWRH demonstrated optimal stabilizing effects due to its excellent compatibility with the LAE-12 base fluid. The emulsion exhibited better stability, characterized by a lower Turbiscan Stability Index (TSI) value and smaller particle size, under the following conditions: an organoclay concentration of 2.0%, an emulsifier concentration of 6%, a calcium chloride concentration of 40%, and an oil-to-water ratio no lower than 75:25. The study also found that while the electrical stability test is convenient, it cannot comprehensively reflect the dynamic stability of the emulsion or the influence of complex factors. In contrast, the multiple light scattering method can more intuitively reveal instability mechanisms such as creaming and coalescence. The findings of this research provide a theoretical basis for the formulation optimization of biomass-based synthetic drilling fluids. It is proposed that combining multiple light scattering with electrical stability tests can establish a more comprehensive evaluation system for emulsion stability, offering theoretical support for the development and iterative improvement of high-performance biomass-based synthetic drilling fluids.