In order to solve the formation control problem for unmanned aerial vehicle (UAV) in a complex environment, a distributed formation controller is designed considering the external disturbance and incomplete feedback of state information. By using the position feedback, a state observer is proposed based on second-order precise differentiator. Then, the velocity of UAV and the estimate of external disturbance are derived. Combining the estimation information and the positions and velocities of its adjacent UAVs, the formation controller and attitude tracking controller are designed based on the continuous twisting sliding mode control method. The stability analysis ensures the stability of UAV’s closed loop system. The control algorithm is verified on the Matlab/Simulink and a software-in-the-loop simulation platform, and the proposed method is verified and demonstrated via 3D visualization.