Cooperative combat task assignment is recently one of the hot spots in military research area, and it is generally divided by previous researchers into two separate phases, namely task pre-assignment and dynamic assignment. However, in this manner the correlation between the aforementioned two phases is to some extent neglected. This article investigates into this issue from the perspective of multi-and single-optimization, and proposes a transform method for multi/single-assignment optimization. Decision-maker's subjective preferences were obtained through their choices in the pre-assignment phase. Based on the acquired subjective preferences, the multi-objective optimization is transformed into single-objective optimization, and then the task re-assignment is completed using contract net protocol. Simulation results verify the proposed transform method as well as its applicability in dynamic assignment problems. Finally, the correlation between traditional multi-and single-objective optimization is demonstrated and a potential future research direction is outlined.