Abstract: The cryocooler working at liquid hydrogen temperature with a large cooling capacity is one of key technolo-gies for hydrogen zero boil-off storage in space.The precooled direct throttling JT cryocooler has advantages of absence of moving parts at low temperature and simplicity.With the potential to provide a large cooling capacity,it can realize longdistance transmission of cooling capacity separately.Meanwhile,the bypass structure is no longer required during the cooldown process.Based on the scheme of direct throttling JT cryocooler,an open-cycle experimental prototype of the direct throttling JT cryocooler working at liquid hydrogen temperature was built which was precooled by the GM cryocooler.Cool-down process was introduced.The cooling capacity of 10.19 W was measured at 20.8 K.