The invention provides a yarn dyeing machine with a 1:2 extremely-low bath ratio. The yarn dyeing machine mainly comprises a yarn cylinder, a liquid collecting pipe, a base, a motor, a volumeter, a cylinder cover, a steam inlet, a steam outlet, liquid supply and discharging pipes, a liquid temperature meter, a high pressure meter, a low pressure meter, a hydro-acupuncture probing sleeve, a heat exchange pipe, a flow distribution disc, a round heaven and square earth pipe, a yarn bamboo pipe, a liquid collecting cavity, a mixed-flow pump, a flow guide pipe and a water baffle and the like. Due to the ingenious structural design, the 1:2 extremely-low bath ratio of the yarn dyeing machine close to the limit can be achieved, auxiliaries and dye are obviously saved, the waste liquid discharge is reduced, and the yarn dyeing machine is very obvious in economic and social benefits. The yarn dyeing machine is compact in structure, a flow channel is short, and the yarn dyeing machine has excellent energy efficiency.