Abstract: Generally, propeller surfaces are made from polished metal and have no antifouling provision, making them vulnerable to biofouling, yet the effects of such fouling on the performance of propellers are rarely studied. The present work simulates the flow field distribution around the fouled blade section by means of CFD. Barnacles are selected as the major subject from the fouling community and are directly modeled on a geometric level. The results show that the fouling causes earlier separation of the boundary layer and increases the separation region, which further leads to significant reduction of the lift-drag ratio (up to about 90% in maximum), and would thus result in remarkable decrease in the propulsive efficiency of propellers. However, when the height of barnacles exceeds a certain limit, their future growth yields limited effects on the lift-drag ratio.