RVR (Runway Visual Range) calculation and estimate methods of illumination threshold and light intensity are summarized, and the estimate methods in the Vaisala AviMet system are discussed in combination with the ICAO (International Civil Aviation Organization) convention Annex 3 (Meteorological Services for International Air Navigation). A method for estimationg illumination thresholds and light intensities in the Vaisala AviMet system is devised by means of historical data. The analysis indicates that the estimate methods of illumination threshold in the Vaisala AviMet system are not in accordance with the formula recommended by ICAO; the light intensity is always set to be 1000 cd instead of the actual value in the Vaisala AviMet system .