The invention discloses a marine riser test bed flange tension device, and relates to a flange tension device of a marine riser test bed for petroleum and gas offshore drilling, and provides a flange tension device for enabling the stressed state and the actual stressed state of a marine riser flange when a marine riser is tested. The marine riser test bed flange tension device comprises a marine riser flange and a blocking flange which are connected by a tension device; the tension device comprises a tension bolt, a tension nut, a driving device, a driving device installation seat and a torque sleeve; the tension bolt and the tension nut form a threaded connecting mechanism together so as to connect the marine riser flange and the blocking flange; the driving device is connected with the blocking flange by the driving device installation seat; the torque sleeve and the driving device are connected; the sleeve is internally provided with a nut hole; the tension nut is positioned in the nut hole and can slide along the nut hole. The marine riser test bed flange tension device disclosed by the invention can be used for the blocking operation of the end surface of the marine riser in marine riser testing.