Abstract: Paired ionization chambers used for the dosimetry of mixed gamma-neutron field in reactor, consist of a tissue-equivalent chamber which responds to both neutron and gamma radiation, and a nonhydrogenous chamber which is relatively insensitive to neutron. In this work, the gamma radiation energy response and response factor of tissue-equivalent chambers under different conditions were calculated by MCNP code for the development of paired chambers. The calculated result is in accordance well with the result in references.