Workflow provides a powerful support to CSCW (Computer Supported Cooperative Work) as an efficient process management tool, one of the most significant contents of workflow is the distribution of tasks, it makes mapping between tasks and individuals. Most of the process-modeling methods are role-based, they make mapping between tasks and roles. Almost all of these methods focus on the decomposition method and logic structure of process, but they ignore the impact of role granularity to process-modeling. The structure of modern enterprise determines that a role has a characteristic of granularity. For one same business process, its structure is not the same to different roles in different granularity levels. A business process needs multi-granularity descriptions accommodate to roles in each granularity. Based on the concept of granularity, a Workflow task distribution model for CSCW is established with the analysis of processes, tasks, roles and individuals. An implementation method is proposed to meet this model, within this method, a business process is described in several granularity levels to fit different roles. An intelligent distribution method of tasks is studied to distribute different tasks in each granularity level.