In order to explore the growth and physiological characteristics of stress resistance in seedling of Viola tricolor under NaHCO₃ stress, we treated the seedlings of V. tricolor with different concentrations of NaHCO₃ ［0 mmol·L^-1 (CK), 25 mmol·L^-1, 50 mmol·L^-1, 100 mmol·L^-1, 150 mmol·L^-1, 200 mmol·L^-1］, and determined the height growth, osmotic regulation substances, antioxidant enzyme activity, photosynthetic pigment content, and malondialdehyde (MDA) content on the 7th day and 14th day. The results showed that: (1) compared with CK, the height growth of V. tricolor was significantly increased when NaHCO₃ concentration was less than 50 mmol·L^-1, and close to CK when NaHCO₃ concentration was 100 mmol·L^-1, but significantly decreased when NaHCO₃ concentration was higher than 100 mmol·L^-1. (2) On the 7th day, the contents of soluble sugar (SS), soluble protein (SP) and free proline (Pro) in V. tricolor leaves were significantly higher under NaHCO₃ treatments than under CK, while on the 14th day, the contents of SS under all NaHCO₃ concentration, SP under 50 mmol·L^-1, Pro under 150 and 200 mmol·L^-1 were significantly higher than under CK. (3) On the 7th day, the activity of superoxide dismutase (SOD) in V. tricolor leaves was significantly increased under NaHCO₃ treatments than under CK, while the activities of peroxidase (POD) and catalase (CAT) had no significant change. On the 14th day, the contents of CAT under all NaHCO₃ concentration, POD under 50 mmol·L^-1, SOD under 100 and 150 mmol·L^-1 were significantly higher than under CK. (4) MDA content in V. tricolor leaves increased gradually with the increase of NaHCO₃ concentration, and was significantly higher than CK. (5) Compared with CK, chlorophyll content in V. tricolor leaves did not change significantly on the 7th day, while decreased significantly under 150 or 200 mmol·L^-1 NaHCO₃ concentration on the 14th day. The results indicated that V. tricolor could tolerate lower than 100 mmol·L^-1NaHCO₃ concentration and NaHCO₃ had a dose effect of promoting plant height growth at low concentration and inhibiting plant height growth at high concentration. V. tricolor could alleviate the peroxidation damage induced by NaHCO₃ stress through increasing the contents of osmotic regulatory substances and enhancing the activities of antioxidant enzymes, and thus improved the tolerance of V. tricolor seedlings.