The invention discloses a river sediment depth measuring device comprising a pneumatic control circuit and a support guide measurement system. The pneumatic control circuit is composed of a pneumatic motor (1), a manual reversing valve (6) and a compressed air storage tank (7). The support guide measurement system is composed of measuring rods (2), a support guide frame (3), a support guide base (4) and a measuring head (5). The top end of the measuring rods (2) is connected with the power output shaft of the pneumatic motor (1), and the bottom end of the measuring rods (2) is connected with the measuring head (5). During operation, the measuring device is installed on a measuring ship, the pneumatic motor (1) makes the measuring rods (2) and the measuring head (5) rotate and drill in through a transmission thread, and when the measuring head (5) drills into the bed of a river, the direction of rotation of the pneumatic motor (1) is changed by the manual reversing valve, the measuring rods (2) and the measuring head (5) are taken out, and the sediment depth of the river is calculated through sediment observation holes according to the number of the measuring rods (2) used.