Focus on one kind of uncertains multi-robot cooperative mission, propose a dynamic optimization approach. At each optimal moment, get the transient mission condition, and the optimal cooperative mission. Decompose the entire systematic path-planning mission into two problems: path planning of individual robot and optimal path assignment problem. The fastest cooperative motion is realized. This method is proved by a simulation example of target movable formation, and it could be easily applied into other uncertain cooperative mission, thus having some degree of generality.