Aiming at the unstable operation of the cryocooler self adjusting mechanism caused by the change of inlet pressure and flow rate of high pressure fluid,the theoretical model of the heat exchanger and self adjusting mechanism in the cooler is established based on the heat balance equation method.The influence of high pressure fluid with various inlet pressure and flow rate on the performance of self adjusting J-T cryocooler is analyzed.The results show that the total pressure drop of high pressure fluid before throttling and the dryness of low pressure fluid after throttling decrease with the increase of inlet pressure but increase with raising flow rate；with the change of inlet pressure and flow rate,there is a peak value of refrigerating capacity；under the increase of inlet pressure and the decrease of flow rate of high pressure fluid,the cold zone of cooler gradually narrows；for the fixed heat exchanger structure in this study,with the change of inlet pressure and flow rate,the needle insertion depth and cone angle have the optimal value.For the cryocooler structure studied in this paper,when the flow rate is less than 0.1g/s,the influence of high pressure fluid inlet pressure (20～30 MPa) on changing the range of needle insertion depth can be ignored.