Abstract: This paper analyzes the safe separation constraint of unmanned aerial vehicles (UAVs) by using the geometric guidance method. The linear constraints are established from the nonlinear safe separation constraint by applying the space mapping method. The conflict resolution problem of heterogeneous UAVs is reduced to a mixed integer linear programming (MILP) model, with the objective of reducing the additional cost by minimizing the summation of deviations from the preferred heading directions. Simulation experiments are presented to demonstrate the proposed algorithm. The results show that the proposed algorithm is efficient to find out conflict free solutions for complicated airspace conflict.