Video processing and analysis have been an interesting field in research and industry. Information detection or retrieval were a challenged task especially with the spread of multimedia applications and the increased number of the video acquisition devices such as the surveillance cameras, phones cameras. These have produced a large amount of video data which are also diversified and complex. This is what makes event detection in video a difficult task. Many video event detection methods were developed which are composed of two fundamental parts: video indexing and video classification. In this paper, we will introduce a new video event detection system based on graphs. Our system models the video frame as a graph in addition to a motion description. Thereafter, these models were classified and events are detected. Experimental results proved the effectiveness and the robustness of our system.