Abstract: By the method of artificial freezing, this paper made a comparative study on the cold hardiness of Pinus ponderosa, P. banksiana and P. tabulaeformis, with their inherent mechanisms approached. The results showed that the cold hardiness of these three species was in the sequence of P. banksiana＞P. tabulaeformis＞P. ponderosa. P. banksiana had high bound water/free water ratio (7.0) and ABA content (164.3 μg·g^-1 FW) but low K⁺ (2 450 μg·g^-1 DW) and soluble sugar (12.0%), P. tabulaeformis had higher contents of ABA (95.8 μg·g^-1 FW), K⁺ (4 538 μg·g^-1 DW) and soluble sugar (18.68%) but low bound water/free water ratio (2.58), while P. ponderosa had high soluble sugar content (18.05%) but low bound water/free water ratio (2.18) and K⁺ (2 275 μg·g^-1 DW) and ABA (63.3 μg·g^-1 FW) contents. These differences might be the reasons resulting in the different cold hardiness of these three species. Low chlorophyll content and high carotenoid/chlorophyll ratio might also contribute to the cold hardiness of P. banksiana. Therefore, though the test species are all of cold hardiness, their inherent mechanisms may be different.