Abstract: This paper summarizes the development work of a big refrigeration capacity two stage G-M refrigerator which uses magnetic material as 2nd regenerator matrix.It gives the results of the theoretical study and the structural design.An experimental study has been done in a sample machine.By optimizing the machine structure and the operating parameters,the no-load temperature of the second stage is 7.8 K.The net cooling capacity 14.5 W has been achieved at 20 K.From the theory and experiment,it explores the effectiveness of the improvement refrigeration performance with magnetic regenerator materials.