The cooling load, which should be removed by the cooling system to maintain the nominal operating temperature of a cryochamber, depends on the thermal insulation efficiency of the cryochamber. Therefore, to decrease and minimize the heat loss of the cryochamber has become a big problem in the design stage, in considering the very low thermal efficiency and small cooling capacity of the cryocooler. Radiation and conduction heat transfer occur simultaneously in a cryochamber. The radiation heat transfer from the hot surface to the cold surface depends on the emissivity, temperature, area and radiation exchange factor. In the present work, the energy equation, which includes the rarefied gas conduction, radiation between the boundary surfaces and solid conduction, is solved to evaluate the steady cooling loads at the cold finger of a small cryocooler. The surface to surface radiation model is used for the calculation of the radiation exchange factor. This paper presents the effects of the emissivity of the materials and the radiation shield on the cooling load of a cryocooler.