The fan blade icing has significant influence on aero-engine rotor unbalance, which may induce the engine power loss. Based on the influence of fan blade icing, the mass of fan blade icing is analyzed by commercial software, and the implicit transient rotordynamic analysis is then conducted to simulate the unbalance of rotor. The influence of the icing on the rotor unbalance is analyzed in details by the whole engine finite element model. Furthermore, the closure of rotor and stator is analyzed, and the most critical condition of fan blade icing is obtained. The results show that the most critical condition of fan blade is idle, and there are influences on the 1# bearing and 2# bearing. This work provides useful design and test guidance for the fan blade icing.