Abstract: Ice accretion of civil aircraft has been a major concern to flight safety.The civil air-craft must show compliance with the airworthness icing regulation to make sure that the aircraft can fly safely under the icing condition.The critical ice shape is the most important input for the evaluation of performance/stability and control under the icing condition,and therefore it must be determined at the very begining of ice certification.Firstly,the standard of the critical ice shape is set up,and the procedure of the critical ice shape determination is proposed.Then,the sensi-tivity of the icing conditions has been analysed by SADRICE code,and the critical icing condition is obtained.Icing wind tunnel tests have been conducted in Italian Aerospace Research Center to verify the critical icing condition.The test results show great agreement with numerical simula-tion results.It is found that MVD= 20μm,RAT= 0℃ is the most critical icing condition for the aircraft under research.Test and numerical resuts of the angle and height of the ice shape upper horn are the same,testifying the correctness of the sensitive analysis and the relevant critical ic-ing condition.The critical ice shape can be used in aircraft icing certification.This is of value to other aircrafts icing certifications.