Abstract: The Gifford-McMahon (G–M) cryocooler system is one of the key components of liquid helium free Josephson voltage standard. However, the electrical characterization of quantum effect is closely related to the surface temperature of the Josephson junction array, and the Josephson junction array chip is highly sensitive to the environmental temperature. Especially, when the surface of the junction array is irradiated with high power microwave, a large number of heat loads aggravate the instability in the liquid helium free environment. In view of the above problems, this paper deeply analyzes and researches the heat conduction characteristics of liquid helium free quantum voltage standard, and proposes a two-stage radiation heat leakage and heat conduction model. By using this model, a cryostat is designed, and the temperature stability and the current-voltage (I–U) characteristics experiments are carried out. For the 2 volt programmable Josephson array chip, the experimental results show the minimum quantum voltage step of each subarray is greater than 1.3 mA, which verifies the accuracy and feasibility of the proposed model. The relevant theories and methods are important basis for the design and improvement of liquid helium free quantum voltage standard system.