Abstract: A sub-channel thermal-hydraulic analysis code named SAAF (sub-channel analyzer for annular fuel) for annular fuel was developed. The thermal-hydraulic properties of annular fuel pins for Westinghouse 4-loop PWR were calculated by SAAF code, and the calculating results of SAAF and VIPRE-01 codes were compared. The results show that the SAAF code can be used to determine the thermal-hydraulic properties of the annular fuel.