The utility model discloses a trench excavation protection device for water conservancy construction, which comprises two protection side plates, the lower side walls of the two protection side plates are both provided with two rotating bottom grooves, the two protection side plates are rotatably connected with supporting bottom rods through the rotating bottom grooves, the upper end of each supporting bottom rod is rotatably connected with a reinforcing supporting rod, and the lower end of each supporting bottom rod is rotatably connected with a supporting rod. The side walls, close to each other, of the two protection side plates are each provided with two side sliding grooves, and adjusting screw rods are in threaded connection with the positions, located on the upper sides of the side sliding grooves, in the upper side walls of the protection side plates. Buffering pads are fixedly connected to the side walls, close to each other, of the two protection side plates, and rotating bases are fixedly connected to the side walls, close to each other, of the two buffering pads. According to the utility model, the adjusting screw rod can drive the sliding block to slide up and down in the side sliding groove, so that the angle between the reinforcing side rod and the protective side plate is adjusted, and the groove on the outer side of the protective side plate can be effectively reinforced.