A new online detection system for bottled beers was presented. The volume of beer was determined by detecting real-time the height of beer in the bottle. The system is mainly used to examine online whether the volume of beer meets the requirements. The system consists of high-speed image sensors with window functions and DSP. The developed software provides a boundary detection algorithm to detect liquid level. The system holds the following features:high detection rate, that is, each bottle detection time is less than 50 ms|nonsensibility to the external lighting and bubbles in bottles|saving photoelectric sensors because of the use of image processing technology positioning beer bottles|small volume, easy to install in the fields.