The decision-making subsystem is the kernel part of the robot-soccer system. By analyzing the strategy of role assignment of robot soccer, the paper has designed a function expression to valuate the capability of controlling the ball of the team-members. After that, a cooperating strategy based on opponent information is proposed, which can assist the shooter much better, avoid obstacle more successfully and destroy opponent attack much more availably. Furthermore, the strategy can enhance the team-members' flexibility and competitive efficiency. Finally, the simulation researches are given to demonstrate that the strategy is feasible and effective