At present, unbonded flexible pipes (UFPs) are widely used in ocean engineering for oil exploitation. In practice, erosion will lead to premature failure of pipelines. There is a lack of researches on the erosion of interlock carcass of UFPs. As the authority in the field of offshore engineering, DET NORSKE VERITAS(DNV) suggested a way to estimate the erosion rate of pipes, however, it does not study the erosion mechanism of UFPs in detail and the relevant parameters are not specified. This paper modifies erosion prediction of UFPs based on a user defined Fortran subroutine. A series of CFD simulations have been conducted, and three widely used erosion models were used for comparative verification. The effect of geometric shape on erosion rate has been carefully studied. and the effect of velocity, particle size, and concentration are also studied to verify the reliability of the improved model.