Phenology is a sensitive indicator of climate change and a key parameter of terrestrial ecosystem model. At present, there are many studies on the impact of climate change on phenology, but there are still few studies on the synergistic effects of climate change and air pollution on leaf yellow phenology, which restricts the cognition of phenological mechanism and model development. In this article, Larix gmelini seedlings with three years old were taken as the research objects by using the controlled experiment to study the response of its leaf yellow period to the changes of temperature, photoperiod, nitrogen addition and their interaction. The results showed that:(1) temperature rising had a significant effect on the leaf yellow stage. Rising temperature significantly advanced initial and common stages of leaf yellow, but did not significantly delay leaf complete discoloration stage. (2) The effect of photoperiod on the leaf yellow stage was very significant. Extension of photoperiod significantly advanced initial and common stages of the leaf yellow, and significantly delayed leaf complete discoloration stage. (3) The correlation between the stage of leaf yellow and nitrogen addition amount was not significant. (4) The interactive effects between temperature, photoperiod, and nitrogen addition on initial and common stages of leaf yellow were extremely significant and had extreme values, but the effects on leaf complete discoloration stage were not significant. The interaction between temperature rising and photoperiodic extension advanced initial and common stages of leaf yellow, and the most significant effect happened at temperature rising of 1.5℃ and photoperiod of 14h. The interaction between photoperiodic extension and nitrogen addition advanced initial and common stages of leaf yellow, and the most significant effect happened at low nitrogen addition (5g N m^-2 a^-1) and photoperiod of 10h. The interaction between temperature rising and nitrogen addition advanced initial and common stages of yellow leaf, and the most significant effect happened at high nitrogen addition (20g N m^-2 a^-1) and temperature rising of 1.5℃. (5) The interactive effects among temperature rising, photoperiod, and nitrogen addition were very significant on initial and common stages of leaf yellow, and not significant on leaf complete discoloration. It indicates that the changes of temperature, photoperiod, and nitrogen addition would prolong the duration of leaf yellow of Larix gmelini seedlings, as a result, the duration of carbon sequestraction would prolong. These results can provide a basis for developing phenological models and estimating carbon sequestration of forest ecosystems.