Abstract: AA356 aluminum alloy has been widely used in aerospace and other fields. However, it is faced with severe tool wear in the process of micro machining and the relevant mechanism is not clear. To reveal the influence mechanism of cutting parameters on the tool wear of CVD diamond tool micro milling AA356 aluminum alloy, micro machining experiments were carried out with orthogonal test design and response surface method. The prediction equation of tool wear was established by using least square method and the particle swarm optimization algorithm. Besides, the mechanism of tool wear and the effect of cutting parameters for tool wear were analyzed. The results show that the main wear mechanisms of micro-tool are coating delamination and adhesive wear induced by complex cutting loads. The main factor of influencing tool wear is the axial cutting depth, followed by the feed speed and the effect of spindle speed on tool wear is minimal. A strong coupling effect can be found between the spindle speed and the feed speed.