The formation flight control problem of multiple fixed-wing unmanned aerial vehicles (UAVs) is studied. Considering the kinematical characteristics of a group of fixed-wing UAVs, the formation graph is introduced to specify the formation geometry, which describes the relative position of any two UAVs with respect to the heading of the group respectively. Based on the formation graph, a decentralized formation flight control strategy via information consensus is presented, which consists of two individual parts, one is to synchronize the motion of UAVs using relative velocities and relative heading angles, while the other is to achieve and maintain the formation geometry using relative positions. Since only local relative state information is needed, this control strategy is easier to realize, with more flexibility and robustness, than any other formation control strategies. Simulation results demonstrate the effectiveness of the proposed formation flight control strategy.