Abstract: On the bases of κ-ε turbulent flow model, it is possible to construct 3D flow-field model to reflect circumferential flows of sea currents around spud legs of offshore platform with riser of subsea pipeline connected with spud legs of offshore platform. By using the model, it is possible to simulate the changes of flow fields and pressures around riser under different conditions during erosion. In addition, the mechanism related to local erosion of riser in subsea pipeline is studied. Research results show that the vertical axial vortex is more and more intensive with the increase of the suspended length of horizontal pipe connected with riser. In addition, local erosion of subsea pipeline is accelerated under such circumstances. Within certain scope, erosion velocity is increased with the increase of the space between spud legs and riser. But as soon as the space is increased to a certain limit, erosion velocity is decelerated. By enlarging the diameters of spud legs, it is possible to reduce the washing volume carried by sea currents, and eventually alleviate erosion.