Nowadays, active power reference of wind farm from power grid dispatch center should be allocated to wind turbines. In traditional way, centralized control is commonly adopted for active power allocation, in which, total power reference is dispatched to every wind turbine by a central controller. However, it has several disadvantages, such as complex computation and low flexibility, especially for wind farms with large number of wind turbines. Therefore, a Multi-Agent based collaboration control strategy for active power dispatching in wind farms is proposed to improve operation performance. Firstly, a Multi-Agent based control structure for wind farm is designed, which includes wind turbine agent, group manager agent and central manager agent. Secondly, coordination control strategy among different agents is designed in detail. Finally, a Multi-Agent control model of wind farm is established based on java/jade platform, and simulation results verify the efficiency of strategy proposed.