With the continued rapid growth of flight traffic and the increasing shortage of civil aviaton airspace resource, to implement the collision avoidance between aircrafts effectively is the key technology to avoid aircrafts collision. A model for the aircraft protecting zone is reasonable constructed and a collision avoidance algorithm based on ADS-B is proposed. This algorithm make full use of the characteristics of high precision and high-speed update rate for the ADS-B message, propose two types of the collision avoidance strategy of ” Keep speed is constant, and change direction” and “Keep direction is constant, and change speed” from horizontal direction and two kinds collision avoidance strategy of “climb” and “descend” from vertical direction. Using the horizontal velocity，direction and vertical speed as control variables, the conversion time of the control variable through the calculation of boundary conditions is obtained, thereby the feasible resolution method is founded. The simulation results show that not all conflict resolution strategy is feasible for the same flight conflict situations, it need to choose the most optimal collision avoidance pattern according to specific situation by pilot from the feasible resolution strategy