Available face detection and evaluation standards are usually only a qualitative detection of the face existing, and have no strict norms for the quantitative description of the face location in videos.In addition, some researches such as video face replacement have higher requirements for the continuity of the face position in the video sequences. To solve these two problems, compared with the previous face detection algorithms and the face tracking evaluation standards, a quantitative detection standard of the human face position in the video was proposed, and a modified method of video face position detection was put forward. The initial face location was firstly detected in the target area by the improved Haar-Like cascade classifier; then the pyramid optical flow method was used to predict the position of the face, at the same time the forward-backward error detection mechanism was introduced to the self-checking of results, and finally the location of human face was determined. The experimental results show that the detection standard can give the evaluation of the quantitative description of the detection algorithm in the video face detection, and the proposed detection algorithm has a great improvement in the time consistency of face position in the detection results.