The invention discloses a broad-gauge universal open wagon with a turn-down type bottom side door, belonging to the technical field of rail wagon manufacturing. The broad-gauge universal open wagon comprises a chassis, a bogie, the bottom side door, a side wall, a pneumatic or manual brake apparatus, an end wall and a car coupler buffer device; a web is welded between an upper cover board and a lower cover board of a middle beam, and the web is a section-variable structure; a side beam is a cold-formed channel steel structure, the web is welded between the upper cover board and the lower cover board of a big cross beam, two webs are installed and welded between the upper cover board and the lower cover board of a sleeper beam, the web is welded between the upper cover board and the lower cover board of a longitudinal beam, and a small cross beam and a cross beam are both cold-formed U-shaped beams; and the bottom side door is of turn-down type. The broad-gauge universal open wagon can effectively reduce self weight, and also can improve carrying capacity, so that service life of a car body is improved, and overhaul period is prolonged. Maintenance work load and transportation cost are reduced greatly, volume of the open wagon is increased, and the open wagon can be linked with the existing vehicle which is provided with a screw coupling. The open wagon can meet the requirements of a broad-gauge railway (track gauge is 1676 mm). The bottom side door is convenient and efficient to operate.