We are studying the neutron production regime in IECF (inertial electrostatic confinement fusion) device. Fusion reactions are mainly occurred both beam-background and fast neutral-background reaction in IECF device. The cross section of D-D reaction increases with incident deuteron’s energy. If the reaction occurs only from beam-background channel, generated neutrons will dominate near the cathode. Two 3He proportional counters which are in lengthwise and lateral positions were used to measure neutron counts. The results showed neutrons were produced via not only beam-background channel but also fast neutral-background channel.