The invention discloses a self-submergence frame type sampling method of marine juvenile fish by a sampling net, which relates to a sampling method of marine juvenile fish and needs to provide a net tool for sampling the marine juvenile fish away from the bottom and a method for controlling sampling depth. The sampling net tool provided for the sampling method is characterized in that a net port of the sampling net tool is welded into a rectangular frame by a steel pipe; four non-section net pieces with meshes of 10mm are cut into trapezoidal net pieces which are wound into shapes of a net bag; a wide port of the net bag is engaged with the rectangular frame; a narrow port of the net bag forms a bag net; the tension length of netting of the net bag is 4 meters; the lower edge of the net port is connected with a submergence device which is made into a framework by the steel pipe; a submergence deflector covers the upwind surface of the framework of the submergence device; both ends of the submergence device are hinged with triangular drawing plates which are connected with a cross rope; upper transverse beams of the net port are all uniformly tied with floaters; ship speed is between 3 knots to 3.5 knots during net placement; and the length of the cross rope is controlled and released gently by operating water depth so that the net tool is placed on an operating water layer to draw the net and sample. The sampling method is suitable for sampling the marine juvenile fish.