To deal with the issue of path planning and formation control for unmanned aerial vehicle (UAV) formation flight, an improved algorithm of path planning and formation control based on three-dimensional artifical potential field (3D-APF) is proposed. For path planning of UAV, an improved 3D-APF is constructed. On this basis, the dynamic model of UAV in the virtual force environment is derived and established. For how to maintain the formation, using constraint dynamic, the constraint dynamic equation set is established by introducing the Lagrange multipliers, which can maintain the desire formation during the whole process. Finally, using Penalty-Formulation to solve the Lagrange multipliers, the constraint dynamic equation for UAV formation flight is obtained. The simulation results based on the Matlab platform show the effectiveness of the algorithm.