The forces on a spherical particle settling in still water with a high Reynolds number were investigated based on the settlement mechanisms of single particles of sediment. The formulas of instantaneous settlement velocity, settlement duration, and settlement displacement during accelerating settlement were deduced. The computational results from the formulas were compared with the experimental results. It was found that the relative errors were all less than 5% between the computational displacement and experimental data, and most of them were less than 4%; and the relative errors were all less than 7% between the computational instantaneous settlement velocity and experimental data, and most of them were less than 5%, indicating that the computational values agreed with the experimental data.