The invention relates to an underwater optical cable cross wall sealing structure which is used for connecting and sealing a communication optical cable quickly in the shallow sea environment. One end of a transition sleeve is in seal connection with a junction box, the other end of the transition sleeve is connected with a tail disc; a cross wall sleeve is in seal connection with the interior of the transition sleeve, one end of the cross wall sleeve internally accommodates a sealing plug, and is in threaded connection with a sealing thread sleeve, the other end of the cross wall sleeve traverses through a tail cover, and is in threaded connection with a clamping thread bush, the clamping thread bush internally accommodates a sealing plug, and is in threaded connection with a sealing thread sleeve; the cross wall sleeve internally accommodates a compaction wedge, and the compaction wedge is arranged between the clamping thread bush and one end of the cross wall sleeve; the compaction wedge hoops an internal layer optical cable tightly through the screwing-in of the clamping thread bush, and the sealing plug in the clamping thread bush and the sealing plug in one end of the cross wall sleeve abut against the internal layer optical cable in a sealing manner respectively through the screwing-in of the sealing thread sleeves which are in threaded connection with the sealing plugs respectively, The underwater optical cable cross wall sealing structure is characterized in that the structure can be installed quickly, and is small in size, and the connecting demand of the underwater optical cable in a restricted space can be satisfied.