The analytical solution of the traditional two-dimensional dispersion test theoretical model cannot describe the tailing phenomenon. Therefore, this paper established an exponential decay model to simulate the C-t curve concentration drop in the two-dimensional dispersion test and verified it by the indoor two-dimensional dispersion test. It is found that the simulation effect is better. By changing the hydraulic gradient and concentration, the significance and change rules of the relevant parameters α, β of the exponential decay model are studied. The results show that α is the rate of change of pollutant concentration with time, and β is the ratio of the initial concentration of the source hole to the peak concentration of the measured hole. The greater the pollutant concentration, the smaller the α value, the slower the decay rate of pollutants, the longer the tail time; the greater the hydraulic gradient, the larger the α value, the faster the pollutant attenuation rate, and the shorter the tailing time, and the β value is independent of the flow rate; the farther away from the source hole, the smaller the α value, the pollutant attenuation, the slower the speed, the longer the tailing time, while the β value becomes larger and larger, and the peak concentration of the C-t curve becomes smaller and smaller.