Due to the existence of double-layer repulsive, van der Waals attractive and mechanical forces between colloidal particles such as clay particles and fine-grained ceramic powders, the variation of net force between two particles with particle separation is highly nonlinear. Dynamic numerical simulation techniques such as the discrete element method (DEM) require that the time step be small enough to represent the largest frequency in the system. This poses difficulty in the analysis of a colloidal system where the values of interparticle stiffness may vary over a broad range. An approximate time-stepping method that is suitable for the analysis of a colloidal system is developed from the multiple time-step (MTS) molecular dynamics (MD). In addition, to capture the nonlinear variation in force-displacement relation, a velocity control strategy is employed. The effectiveness of the method is demonstrated by applying it to the discrete element analysis of a clay suspension. It is shown that the MTS scheme presented here is about 3-6 times faster than the regular time-stepping scheme.