The invention discloses a weft selecting mechanism for big tows. The mechanism includes a rapier clamping head and a multi-selection turntable; the multi-selection turntable is provided with multipleyarn guiding channels which can run through big tow fibers; by rotating the multi-selection turntable, the yarn discharging end of each yarn guiding channel can correspond to a clamping part of the rapier clamping head in sequence; a motor is adopted for locating, and conversion of the tows is fast and accurate.