The present invention discloses a method for encoding a flag of an image while encoding an I Frame, firstly setting a start code of an I Frame picture to be coded, for marking a start of the I Frame; setting a flag for indicating whether to code an identification field; judging the set flag, and if the flag indicates to encode the identification field of time and control code of a video tape recorder, encoding the identification field of time and control code of the video tape recorder, otherwise, not encoding the identification field of time and control code of the video tape recorder. In the present invention, the start code is added into the prediction picture header for marking the start of one frame picture data, as well as identifying whether there is the time_code identification field in the picture by the flag information of the time_code identification field, which can realize the objective of identifying the time_code identification field, and avoid encoding additional identification information, therefore it improves coding efficiency, and can be applied to all kinds of video/audio technical standards.