Abstract: A flat energy response characteristics is required for the gas filled ionization chamber used in environmental gamma radiation monitoring. In the paper the dependent of the energy response on the factors such as the volume, wall, gas, electrode, shielding materials and its thickness and area of the spherical argon filled chamber of stainless steel are studied by Monte-Carlo simulation method,. The aim is to reach a energy response with variation less then ±30% over the energy range from 65 keV to 6 MeV.