Risk of the collision of FPSO boardside risers was researched by using the risk matrix method and typical collision accidents were studied about its risk level as well as solutions. Finite element models were established for the replenishment ship, FPSO boardside riser and fendering device by the nonlinear FEM software LS-DYNA. Structure damage deformation, energy absorption and transformation were abtained and then consequence level was divided. According to the historical data of relevant sea area, the frequency of ship collision was determined. The results indicated that cruising speed of the supply ship near the side riser should be controlled within 0.32m/s and the fendering device can be fairly effective to low down the risk level of ship collision.