Abstract: This paper presents a simulation method of the dust wash-off process using sediment dynamics theory to clarify the physical mechanism of the Sartor-Boyd exponential model for the dust wash-off process.Related theories including the non-equilibrium transport model for non-uniform sediment and the delayed response model for sediment transport rate during fluvial processes were summarized, and compared with the Sartor-Boyd exponential model. The comparison revealed that the Sartor-Boyd exponential model is formally equivalent to the delayed response model of sediment transport rate during the clear-water scouring process. Given the delayed effect of rainwater conflux, and the non-equilibrium wash-off characteristics of group-sized dust, a non-equilibrium wash-off model for non-uniform dust was proposed and applied to simulate the dust wash-off processes with different rainfall-runoffs in the Niushan industrial district of Dongguan City, Guangdong Province. Comparison of the application and effects indicated that the estimated dust concentration values using the proposed model were more consistent with the measured values than those calculated using the Sartor-Boyd exponential model; furthermore, the determination coefficient and Nash-Sutcliffe coefficient of efficiency increased from 0.15 to 0.73 and from 0.59 to 0.70, respectively. The results of this research provide a physical basis for the simulation of the dust wash-off process.