The time-marching technique is a strategy for solving time-dependent differential equations. It involves propagating the solution from one time step to the next.The basic principle of time marching is to start with a guessed flow distribution and integrate the time-dependent equations of motion and energy forward with time until a steady-state solution is obtained.

The time-marching CFD technique is essentially suitable to fluid dynamics. Almost all fluid motions are unsteady. Almost steady flow also contains unsteady aspects, especially when the Reynolds number is high and turbulence occurs.