The invention provides an automobile trunk door system, comprising an automobile body, a hinge support and a door. The door includes a top panel and a side panel that are split; the side panel is integrated to the automobile body and is positioned right below the outer edge, far away from the automobile body, of the top panel; sheets of the hinge support are arc arm carriers, including a first armcarrier and a second arm carrier; the first arm carrier is fixed to the automobile body; the second arm carrier is fixed to the top panel and is positioned on one of two sides of the top panel perpendicular to the direction of the automobile body. The automobile trunk door system has the advantages the trunk door is split and is opened sidewise, and therefore, space of an automobile trunk is utilized more efficiently.