Abstract: Placing the cold head at the upper position can facilitate the connection of the with the super_conducting devices.However,for G-M type PTR,the gravity has the disadvantage influence on this situation.For double inlet PTR,DC flow and coupling heat transfer affect the performance of the refrigerator together.The experimental results of G-M type co-axial PTR at the temperature range of liquid nitrogen with the focus on the temperature profile of the regenerator are presented and the effect of the gravity on the perfomance of the PTR is described.