Abstract: In order to study the influence of the cold head structure in the G-M cryocooler with large cooling capacity and mass flow on the cooling performance,discover the internal change law,provide experimental data and theoretical basis for the actual design,the calculation model is established,the experimental is built,and a new structure is proposed to increase the heat transfer area. The research results show that there is an optimal value for the gap thickness,the gap length is about 30 mm and the cooling performance is better. By adding a new convex platform,the cooling capacity at 70 K is significantly increased. It has guiding significance for the development of large cooling capacity G-M cryocooler.