The invention discloses a continuous conveying system and method for a non-equal-diameter detection cable for directional long drilling in an underground coal mine. The continuous conveying system comprises a conveying channel unit and a conveyed unit, wherein the conveying channel unit comprises a cable feeder, a drill rod and a drill bit which are coaxial and sequentially connected; the conveyedunit comprises conveyers capable of moving in the drill rod, and sequentially arranged in a direction from the drill rod to the drill bit, and suspension devices used for connecting the end part of the cable, and capable of being suspended on a drilling wall to fix the cable; and a cavity body between a first opening-closing valve element and an annular sealing element is a sealed cavity body, and water is enabled to enter the sealed cavity body from a water inlet hole and then push the conveyers to drive the cable to move forwards. After a pump is started to pump water, the high-pressure water enters the sealed cavity body from the water inlet hole, and the conveyers drive the cable to move towards a hole bottom direction under the action of a water pressure. The continuous conveying system and method realize the function of remote in-hole detection cable descending for directional long drilling in the underground coal mine, and also realizes the purpose of continuous sealing for thenon-equal-diameter cable in the conveying process, so that the automation level and efficiency of cable descending are increased.