Abstract: The aerodynamic characteristic of a civil aircraft nacelle with foreign object damage (FOD) is numerically simulated which is motivated by the engine/airframe airworthiness validation. The effects of FOD to nacelle internal and external flow characteristics and their underlying flow physics are investigated. The results suggest that: The in-fluence of FOD on the nacelle aerodynamic characteristics and the safety performance can be preferably learned in the investigation which are based on the three-dimensional finite element simulation of collision impact conducted beforehand; The damage and deformation of the cowl results a reduced outflow quality and affects the through flow capacity of the inlet and further reduces the engine efficiency, while resulting a loss of suction at the lip which leads to even greater drag coefficient of nacelle with FOD than the smooth one. Although, the drag coefficients in general are becoming similar between the two when the outflow are stall at the cowl of nacelle. The study also indicates that, the numerical simulation performed in this paper will significantly benefit and provide a technical basis and some recommendations to the safety assessment of the civil aircraft and structural design of the engine nacelle.