Abstract: As is well known, it is necessary to make correction for tube surface temperature measured by pyrometer. Because the reflected radiation has much effect on this temperature, the geometric factor considering the reflected radiation is an important quantity in the temperature correction. This paper presents a new method for calculation of geometric factor F. Based on local angle coefficient, the geometric factor F is obtained by calculating the average angle coefficient in the circle of vision field. As an example, the geometric factors for the Topsφes converter and the Lummus cracking furnace have been calculated, and by comparison of the calculated values of geometric factors for the Topsφes converter with those suggested good agreement between them has been found. Based on the presented geometric factor in this paper, the corrected values for the measured temperature by pyrometer agrees with measured temperature by armor thermocouple.