The systematic analysis is made on the blocking cause of color-change valve and the source of impurity particles,and corresponding solutions is pointed out,such as connecting supply pipe and return pipe immediately to clean paint system by means of short plastic hose,while the robot pipe would be reverse direction flushed separately to discharge particles.Moreover,the Y-shaped filter is installed at the end of paint material supply pipe,which could keep particles from arriving at the color-change valve,so the problem of color mixture could be eliminated effectively.