Abstract: In the simulation of space atomic oxygen(AO) effects, it is essential to determine the parameters in the AO undercutting model. An analysis is made to find out the roles of the parameters in an atomic oxygen undercutting model developed by B. A. Banks. Based on the proposed similarity law, a method is presented to determine the parameters in that model by combining experimental and numerical data. In addition, a new property parameter named the theoretical erosion yield of material is proposed, and the value of which is calculated for carbon fiber epoxy composite. This parameter can be used to establish a link between the simulation result and the experimental result.