The invention provides a yarn tension adjusting mechanism for a two-for-one twister; the yarn tension adjusting mechanism is characterized by comprising a lower bottom plate and an upper top plate; the upper top surface of the lower bottom plate is provided with a plurality of lower supporting seats and lower connecting rods, tension adjusting rollers are arranged above the lower supporting seats,traction rollers are arranged above the lower connecting rods, a plurality of upper supporting seats and upper connecting rods are arranged on the lower bottom surface of the upper top plate, tensionadjusting rollers are arranged below the upper supporting seats, and traction rollers are arranged below the upper connecting rods. Compared with the prior art, the yarn tension adjusting mechanism for the two-for-one twister is reasonable in structure; a yarn is pressed on the tension adjusting rollers through the design of the tension adjusting rollers, the upper supporting seat, the lower supporting seats and telescopic rods, so that the tension of the yarn is changed, and the length of the telescopic rods helps adjust the tension of the yarn; the traction rollers and upper and lower connecting posts can provide drawing and fixing for the yarn, so that the yarn can stably move forwards.