Abstract: The structure of the ionization chamber which is used for 6 MeV electron linac (stationary wave) for non-destructive-testing is double sealed and it has two effective sensitive volumes. The features of this ionization chamber are high sensitivity, better saturation and better stability. When the dose rate at a place on the axis and 1 m from the target of linac is 50 cGy/min and the ionization chamber is placed in front of the target about 135. 5 mm, the ionization current is about 1 ×10-7 A. At the same time the leak electric current is smaller than 5×10-13 A. Its absorption to X-ray is less than 1%.