The invention relates to an automatic labeling device for a material bag sewing conveying belt line. The automatic labeling device is arranged on a conveying belt line of a material bag sewing process and is mainly composed of a rack body assembly (1), a stamping assembly (2), a label sending assembly (3) and a blocking arm assembly (4), wherein the stamping assembly (2), the label sending assembly (3) and the blocking arm assembly (4) are arranged above the rack body assembly (1), and the stamping assembly (2) is used for stamping a time stamp on a label. When a material bag passes through the conveying belt line so as to be sent in front of the automatic labeling device, a blocking arm (44) in the blocking arm assembly (4) protrudes, so that a movable plate (12) in the rack body assembly (1) advances at the same speed of the material bag, the material bag and the movable plate (12) are kept relatively stationary, and after labeling, the movable plate (12) returns to the initial position to wait for the next pack of materials; in the process that the material bag is conveyed, the label with the time stamp is sent to an opening of the material bag by the label sending assembly (3), and the blocking arm (44) retracts, so that the automatic labeling operation is completed.