An improved layered hidden Markov model（LHMM） and entropy value of real-time detection method for gathering abnormal event detection is presented.The video frame is preprocessed using histogram equalization to increase image quality;the number of people and the total speed of people in block area as the observed values

then gathering event’s LHMM in two levels is trained.When the similarity between observation sequences and the model is greater than certain threshold

then calculate the entropy of the frame by using optical flow method.When the entropy value is greater than the certain threshold

a gathering event is judged to happen;otherwise

it is not a gathering event and continues to process next frame.A large number of experimental results show that the proposed method has higher recognition rate

better robustness and high processing speed and wider applications.