Abstract: This article introduced the parallel grid ionization chamber that used to measure the α radioactivity, which had a independent vacuum system. The system was composed of main body of the chamber, gas-filled and electronics system. Energy resolution was 26 keV for ²³⁹Pu, background was 10 counts for one hour from 4 MeV to 6 MeV energy range, the stability of 24 hours was less than 0.5%. The chamber can measure the energy of nuclide and analyze the energy spectrum structure to identify nuclear.