In this paper， a control strategy based on bearing-only measurements is designed for the velocity-tracking formation control of an unmanned aerial vehicle （UAV） swarm. The controller design of UAVs only depends on the relative bearing of an adjacent UAV， which can be applied to a situation where the communication of the UAV swarm is blocked. The velocity tracking of the UAV swarm formation system is achieved by the design of the proportional integral controller based on bearing-only measurements. The stability of the controller is analyzed by the basic Lyapunov function， which is more conducive to the extension and application of the control strategy to more complex situations than the method based on the optimization strategy and continuous excitation. Finally， the effectiveness of the proposed control method is verified by fixed and velocity-tracking formation control simulations.