According to the national classified protection of information system, information systems whose levels are above three must provide mandatory access control and label. Due to rigid access control rules, existing mandatory access control models are difficult to satisfy the new requirements of collaborative environment. In this paper, we firstly analyze the requirements of access control in collaborative environment. Then, we propose the access control policies according to a very popular scenario. And then, we propose a mandatory access control model with collaboration supported and prove the security of the model by noninterference theory. At last, we compare this models with other related models, and use an application example to show the application of this model. In general, this model integrates task-centric access control with the subject-object-centric access control. The flexibility of the model is greatly enhanced and this model can be considered as an active access control model which is more perfect to be used in collaborative environment. Through controlling the security label of subjects and objects, the bi-directional information flow which is compliant with security policies is solved.