Abstract: The paper describes the theoretical models of coupl in g MCNP and ORIGEN--MCBurn. A PWR pin cell benchmark burnup calculation probl em of 3 burnup cases is used to verify MCBurn. It is concluded that the result s of MCBurn on reactivity and isotopic compositions are in good agreement with t hose obtained from measurement and/or calculated by other codes. Moreover, MCBur n is superior to the similar codes such as MOCUP or Monteburns as far as some of calculating results, the parameter choice and determination as well as the program automatic run are concerned.