Under the premise of limited defense budget, a system contribution rate evaluation method based on the operational loop theory for multi-task considering the influence of cost factors on contribution rate is proposed. Firstly, the capability index system is established and the equipment contribution rate evaluation framework is put forward. Secondly, the weaponry system of system combat capability evaluation model based on the operational loop is established. It is noteworthy that cost factor has been taken into account. Introducing the concept of interval number, a multi-task oriented contribution rate evaluation method for weapon equipment system of system is proposed. Then, the ranking result of development equipment is obtained according to the contribution rate. Finally, taking the maritime warfare as an example, the evaluation method proposed is applied to providing decision support for equipment development.