Abstract: Electrical field in cylindrical proportional counter (PC) was analyzed by using Diethorn formula. It can be seen that multiplication in homemade cylindrical PC happens within the range of less than 30 μm from anode. The lowest operating voltage of the PC is 370-670 V, and it increases with the diameter of both anode and cathode, but changes slowly with the latter. A thinner anode can lead to stronger field around itself, and a lower working pressure will lead to larger mean free path. Both of them can improve the multiplication factor due to the generation of more and more secondary electrons in PC. Selecting a thin anode and low working pressure can not only reduce the lowest operating voltage, but also optimize the performance of amplification of PC, which makes it more suitable to measure radiation dose in deep space.