Abstract: Flows over porous media are frequently encountered in industrial applications such as chemical engineering process and porous particles suspension. It's of great importance to evaluate the force between the fluid and the objects accurately. The momentum exchange method which is efficient and easy for implementation is widely used to determine the force in lattice Boltzmann method. In this work we propose an efficient momentum exchange method to calculate the force by analyzing the exchange process of the fluid and the object. The method is validated by simulating the flows over a porous object at the pore scale, and the method is also extended for fluid-object interaction at scale. Simulations of flows over a square cylinder at different Reynolds numbers are conducted, and the viability of the method is confirmed by the numerical results.