A yarn debris removing apparatus for circular discoloration knitting machines provides compressed air through an air compressor. The compressed air is delivered to a negative pressure generator through a rotary connector that controls the flow direction of the compressed air so that a negative pressure suction nozzle forms a negative pressure to generate a suction force to suck yarn debris cut off on a circular discoloration knitting machine. The negative pressure generator is connected to a dust collection net on another end through a hose to collect and filter out the yarn debris to reproduce clean air. Through the rotary connector the dust collection net and the negative pressure generator can be rotated with the circular discoloration knitting machine. The suction nozzle of the negative pressure generator is directed towards the needles of the circular discoloration knitting machine where change of yarns takes place to suck the yarn debris.