Abstract: In an augmented reality system virtual objects generated by computer are superimposed on the real scene around users, therefore the illumination consistency between virtual objects and real surroundings is one of the key problems. Existing researches on illumination consistency include illumination estimation, material surface reflectance estimation, photorealistic rendering and so on. The illumination estimation is the prerequisite of illumination consistency and guarantees the consistence of illuminations between virtual and real objects while combining with material surface reflectance estimation. This paper summarizes the most recent research progresses on illumination consistency in augmented reality, discusses the main challenges by analyzing the advantages and shortcomings of existing techniques, and predicts the future trends of the illumination estimation in augmented reality.