The invention provides side door locking mechanisms for a double-flap open carriage, which belong to the technical field of vehicle components. The double-flap open carriage comprises a carriage body and double-flap doors, wherein each double-flap door comprises a first door body and a second door body; the first door body corresponds to the upper part of a carriage cavity; the lower ends of lifting arms are respectively hinged with the end surfaces at the two ends of the first door body, and the upper ends of the lifting arms are connected with power; the second door body corresponds to the lower part of the carriage cavity; one side of the second door body is in pivot connection with the first door body, and the two ends of the other side of the second door body are respectively connected with the lower ends of traction rods; the upper ends of the traction rods are matched with sliding tracks through traction rod sliding blocks; the number of the side door locking mechanisms is equal to the number of the lifting arms; and each side door locking mechanism comprises an acting cylinder, a bolt and a bolt sliding sleeve, wherein the acting cylinder is fixed on one side of the carriage body facing to the carriage cavity; the bolt sliding sleeve is fixed on one side of the carriage body facing to the carriage cavity; the lower end of the bolt is connected with an acting cylinder column, and the upper end of the bolt is matched with a bolt sliding sleeve cavity of the bolt sliding sleeve; and latch hooks are formed at the lower ends of the lifting arms. The side door locking mechanisms have the advantages as follows: the action transmission links are less, reliable locking can be achieved, fast opening and locking can be achieved, and the structure is simple.