In the research of cryogenic physics and quantum information science, it is essential to maintain a steady low temperature of millikelvin regime continuously. Dilution refrigerator is a widely used refrigeration device to achieve extremely low temperature. It utilizes the phase separation effect of superfluid ⁴He and its isotope ³He mixed solution at ultra-low temperatures. The performance of heat exchanger is the key factor to determine the performance of continuous cycle refrigerating machine. At extremely low temperatures, there appears a huge interfacial thermal resistance between helium and metal (Kapitza resistance), and the problem of heat exchange can be effectively solved by using the porous sintered metal particles to increase the contact area. Therefore, it is of significance to study the heat exchange between metal particles and liquid helium at extremely low temperature and to develop the relevant high-performance sintered Ag powder heat exchanger.