Abstract: According to the basic structure, working principle and application conditions of the vibration screen jig, the formation access of the screen underflow wa s analyzed.The paper had an introduction on the crushing phenomenon occurred in the process of the screen underflow, the abrasive phenomenon of the related struct ure parts and the influence to the screen underflow.The paper pointed out that the through screen and screen underflow would be two different conceptions.The paper h ad a definition on the components of the screen underflow of the vibration screen jig and introduced the conception of the escapes.Finally, an analysis and study was C onducted on the problems existed in the screen underflow of the present vibration screen jig and the influences to the separation technique and the access and method to reduce the screen underflow of the vibration screen jig was provided.