Based on the mass conservation law and momentum equations of incompressible fluid, the general equation for fluid flow in marching solution is established and the marching solution for flaid flow in manifolds is presented. During the process of marching solution, only an algebraic equation about the fluid speed in branch pipes is solved in a marching step, so it is simple and good in convergence. An example shows that the marching solution is an efficient calculating method for the L style manifolds.