The invention provides a constant-tension and autonomous straightening paying-off device attached to a direct-buried cable paying-off vehicle. The problems that an existing paying-off vehicle is largein paying-off operation difficulty and unsuitable for direct-buried laying are effectively solved. The constant-tension and autonomous straightening paying-off device comprises a bracket, two side plates are mounted on the bracket, a line roller is mounted on the side plates, two guiding rods and a reciprocating lead screw are mounted on the two side plates, an engine of the paying-off vehicle isconnected with a rotating wheel of the reciprocating lead screw through a transmission belt, the guiding rods and the reciprocating lead screw are used for supporting and mounting a paying-off straightening device, a motor is mounted on the side wall of a rack of the paying-off straightening device, two pairs of longitudinal pressing wheels and transverse pressing wheels which are mounted correspondingly are mounted inside the rack, and the motor is connected with the longitudinal pressing wheels in a belt transmission mode. The constant-tension and autonomous straightening paying-off devicehas the beneficial effects that a reciprocating moving device and a bidirectional pressing wheel paying-off device are arranged in one device, and the purpose of constant-tension and straightening paying-off can be achieved through one device.