[en] The Japan Atomic Energy Research Institute (JAERI) has been planning the construction of High Temperature Engineering Test Reactor (HTTR) which in 30MW in thermal power, 850degC and 950degC in outlet coolant temperature and 40kg/cm²G in primary coolant pressure. In the HTTR, coolant flows upward in channels between core and Reactor Pressure Vessel (RPV), then mixed in the upper plenum and flows into the core. This report presents the evaluation results of the core inlet temperature, which is a fundamental value of maximum fuel temperature calculation. Temperature behavior at the core side channel is calculated by FEM code and temperature mixing characteristics is calculated by thermal-hydraulic code 'STREAM'. The evaluation error of core inlet temperature is one of the hot spot factors for the maximum fuel temperature calculation. (author)