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Thermal conditions, such as thermal growing degree-days (GDD) and growing season (GS), have primary effects on vegetation growth. In this study, changes in GDD and GS during 1961-2099 in China have been projected using the daily mean temperatures derived from five general circulation models. The multi-model mean values generally capture the spatio-temporal changes in GDD and GS during 1961-2005 and are thus used for predicting the thermal conditions in the 21st century under the representative concentration pathway scenarios (RCPs). The GDD and GS are found to increase with warming, with stronger GDD enhancement in south and southwest China and larger GS extension in the eastern and southern parts of the Tibetan Plateau. On average, nationally, the GDD increase and GS extension in the long term (2071-2099) range from 279.1 degrees C.d and 16.5 days for RCP 2.6 to 964.4 degrees C.d and 50.3 days for RCP 8.5, relative to 1981-2010. Advances in the start of the growing season would drive the GS extension in the mountainous area in northeast China, as well as south and southwest China. On the contrary, the delay at the end of the growing season would drive the GS extension in northwest China and the regions between northeast China and the tropic of Cancer. An analysis under RCP 8.5 suggests that the temperature sensitivity of GDD would increase from the near term (2011-2040) to the long term for the eastern monsoon zone (237.5 to 262.1 degrees C.d/degrees C) and the northwest arid/semi-arid zone (162.3 to 184.0 degrees C.d/degrees C). However, the sensitivity of GS to the warming would decrease from 10.9 to 8.4 days/degrees C and 9.1 to 6.8 days/degrees C for these two regions, respectively. As thermal conditions intensify, temperature zones in eastern China would progressively shift northward.