The invention discloses a high-gain energy-saving type deep refrigeration machine. The high-gain energy-saving type deep refrigeration machine comprises a helium compressor (1) and an expansion machine. The expansion machine comprises a high-pressure cavity (3) communicating with the helium compressor through a gas inlet pipe (2). The tail end of the high-pressure cavity is fixedly connected with a cylinder (5) with a cold header heat exchanger (4). A filling cavity (8) which is driven by a motor (6) and a transmission shaft (7) and has an opening right opposite to the gas inlet pipe is formed in the high-pressure cavity. The tail end of the filing cavity is fixedly provided with a piston (10) in a connected manner through a corrugated pipe (9), wherein the piston (10) can move up and down in the cylinder. A high-pressure gas inlet passageway (11) and a low-pressure exhaust passageway (12) are arranged in a piston. The high-gain energy-saving type deep refrigeration machine has the beneficial effects that the source of the expansion force of the expansion machine is provided by the motor and high-pressure helium together, the requirement of the industrial production for the large pumping speed can be met, the use degree of the high-pressure helium is high, the cyclic utilization of the helium can be achieved immediately after the high-pressure cavity is filled with the high-pressure helium, the refrigeration efficiency within the unit time is improved, and the loss of the helium is reduced.