The aim of this paper was to select and evaluate the stability of seven candidate reference genes (PD-E1, TUA2, UBQ, ACT2, TUB, HIS and 18S RNA) under three different conditions for RT-qPCR analysis. Cuttings of Populus yunnanensis were cultured in water by two ways, upright and inverted vertically. Different internode barks were collected as test materials from 0 day to 49 day, once in seven day. Upright samples (U) and inverted samples (I) are two different conditions, total samples (U + I) means the third condition. Seven candidate reference genes (PD-E1, TUA2, UBQ, ACT2, TUB, HIS and 18S RNA) were amplified by RT-qPCR. geNorm, NormFinder, BestKeeper and RankAggreg programs were used to select and evaluate the stability of seven candidate reference genes under three different conditions.