An engineering method was presented to deal with the problems of aircraft flight performance affected by ice accretion. Based on the calculation method placing linear varying strength vortex panels on airfoil contour, ice accretion shapes on the leading edges of airfoils were predicted. While computing aircraft flight performance affected by ice accretion, the numerical simulation method was used to solve RANS(Reynolds averaged Navier-Stokes) equations of RNG (renormalization group) ��k-ε�� turbulence model and calculate the flow field characteristics of the whole aircraft. Flight performance, including lift and drag characteristics, was obtained according to the simulation results. The lift and drag penalties showed that ice accretion can worsen aircraft flight performance severely. The agreement of this conclusion with some experimental results indicates that this method could be applied into engineering field to estimate aircraft flight performance which is affected by ice accretion quickly and effectively, and to provide references for developing de-icing technologies and improvement of the aircraft flight performance.