At the basis of analyzing the target assignment mechanism, the discussion about the suitability of target assignment in the task of air and missile defense is given. Because the ballistic missile targets have clear goals and need short response time, a distributed mechanism is adopted and analyzed through modeling with market bidding algorithm; while the aerodynamic targets have more uncertain factors and need longer response time, a centralized mechanism is chosen and analyzed through modeling with improved genetic algorithm. Combining two mechanisms finally, the mixed mechanism of dynamical target assignment is presented for the task of air and missile defense. A simulation example is demonstrated，and the result shows that the mixed coordinate mechanism could deal with large numbers of ballistic missile targets and aerodynamic targets. The mechanism also could deal in some ways, when saturation attacks coming.