A transmission gear mechanism for realizing folding and unfolding of two adjacent panel bodies, wherein end portions of two adjacent sides of two adjacent panel bodies enclose to form a mounting opening into which the transmission gear mechanism is suitable for being installed; wherein the transmission gear mechanism comprises: a housing having a receiving cavity therein, the housing suitable for being installed in the mounting opening; a first gear located in the receiving cavity and suitable for being installed on one of the two adjacent panel bodies; and a second gear meshed with the first gear, the second gear being located in the receiving cavity and suitable for being installed on the other of the two adjacent panel bodies, characterized in that, an end face of an inner end of the housing is provided with two through holes at intervals for two screws to pass through and is provided with two annular water stop ribs, the inner end is an end of the housing suitable for facing the two adjacent panel bodies, each of the annular water stop ribs is suitable for being inserted into one of two annular water stop grooves provided on a top wall of the mounting opening, each of two sets of annular water stop ribs and annular water stop grooves is arranged around one of the two through holes; or an end face of an inner end of the housing is provided with two through holes at intervals for two screws to pass through and is provided with two annular water stop grooves, the inner end is an end of the housing suitable for facing the two adjacent panel bodies, each of the annular water stop grooves is suitable for receiving one of two annular water stop ribs provided on a top wall of the mounting opening, each of two sets of annular water stop ribs and annular water stop grooves is arranged around one of the two through holes. a housing having a receiving cavity therein, the housing suitable for being installed in the mounting opening; a first gear located in the receiving cavity and suitable for being installed on one of the two adjacent panel bodies; and a second gear meshed with the first gear, the second gear being located in the receiving cavity and suitable for being installed on the other of the two adjacent panel bodies, characterized in that, an end face of an inner end of the housing is provided with two through holes at intervals for two screws to pass through and is provided with two annular water stop ribs, the inner end is an end of the housing suitable for facing the two adjacent panel bodies, each of the annular water stop ribs is suitable for being inserted into one of two annular water stop grooves provided on a top wall of the mounting opening, each of two sets of annular water stop ribs and annular water stop grooves is arranged around one of the two through holes; or an end face of an inner end of the housing is provided with two through holes at intervals for two screws to pass through and is provided with two annular water stop grooves, the inner end is an end of the housing suitable for facing the two adjacent panel bodies, each of the annular water stop grooves is suitable for receiving one of two annular water stop ribs provided on a top wall of the mounting opening, each of two sets of annular water stop ribs and annular water stop grooves is arranged around one of the two through holes.