There is short of reliable methods to determine typical elements’ reference luminance at tunnel portals in a certain area. In order to solve this problem, the measured data of luminous climate of a year in Chongqing was firstly used to investigate the reflection of vertical illuminance on the typical elements’ luminance. The influencing factors were studied to develop the mathematical models of vertical conversion luminous efficacy and clearness index as well as solar altitude in four directions. Compared with the data collected inanother year in Chongqing, model shows relatively high precision. On the base of long-term continuous measurement of solar radiation and weather conditions among the luminous climate data, this method could be used to determine typical elements’ reference luminance at tunnel portals effectively and relatively accurately.