The study on microscopic effects of interactions between “Ultrafine Particles”, ranging from 0.001 to 1 μm in diameter in soil has so far not aroused much attention due to limitation in measuring means. Conditions were discussed for application of the laser light scattering technology in the study of interactions between Ultrafine Particles in soil, from the aspects of scattering angle and soil particle density in suspension, and aggregation kinetics of soil colloidal particles and structural characteristics of the aggregates thus formed explored. Results show that (1) for the suspension of yellow earth sample, its proper scattering angle ranges from 90° to 135° and its initial particle concentration in suspension from 1.90×10^-3 g L^-1to 0.119 g L^-1; (2) in the condition that the autocorrelation function curve declines smoothly to the baseline and the scattered light intensity keeps constant with the time going on, the dynamic light scattering technique can be used to determine precisely variation of effective diameter, most probable particle size and particle size distribution during the process of aggregation of soil colloidal particles; and (3) in the system of 298 K in temperature and 90 mmol L^-1 KNO₃ in electrolyte concentration, the aggregation mechanism of the yellow earth particles in suspension was found to be the diffusion-limited cluster-cluster aggregation (DLCA) process with the dynamic light scattering technique, and its fractal dimension of the aggregates formed therein was determined to be 1.56±0.02 with the static light scattering technique.