The invention discloses a rapier loom noncircular gear planetary gear train weft insertion mechanism. The invention is characterized in that planetary carriers are driven by a main shaft of the loom; a drive noncircular sun gear is moveably sleeved on a driven noncircular sun gear shaft, and the drive noncircular sun gear is fixed and can not move; planetary shafts are driven by the planetary carrier; two noncircular gears are fixedly connected on the planetary shafts, one of noncircular gears is engaged with the drive noncircular sun gear, and the other is engaged with the driven noncircularsun gear; and the driven noncircular sun gear outputs motive power, and then the movement and the motive power of the main shaft of the loom are transferred to a rapier gripper by cylindrical gear drive, bevel gear drive and engagement of a rapier wheel and a rapier tape. A noncircular gear planetary train, the cylindrical gear and a bevel gear mechanism are used to transform uniform rotation of the main shaft of the loom to non-uniform reciprocating movement of the rapier gripper. Optimizing the drive ratio function of the noncircular gear can lead an acceleration rule of the rapier gripper to be an isosceles trapezoid to reduce tension of weft. Relay weft insertion can be achieved through different initial phase angles of the planetary carriers in weft insertion mechanisms symmetricallyarranged at the left side and the right side of the rapier loom.