To determine the effects of carboxymethyl chitosan on plant growth and nutrient uptake, Prunus davidiana seedlings were treated with various concentrations of carboxymethyl chitosan. The biomass, physiological characteristics, and nutrient uptake of the treated P. davidiana seedlings were then examined. Compared with the control seedlings, the carboxymethyl chitosan-treated seedlings had a higher biomass and a greater abundance of photosynthetic pigments (i.e., chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid), with the best concentration as 2 g/L carboxymethyl chitosan, which increased the shoot biomass and total chlorophyll content by 26.75% and 24.64%, respectively. Moreover, the application of carboxymethyl chitosan enhanced superoxide dismutase and catalase activities, increased the soluble protein content, and decreased the malondialdehyde and proline contents of the P. davidiana seedlings to some extent. Additionally, the carboxymethyl chitosan treatments decreased the total nitrogen content, but increased the total phosphorus and potassium contents in P. davidiana seedlings to some extent. The minimum of total nitrogen content and the maximum of total phosphorus and potassium contents in shoots of P. davidiana seedlings were the concentration of 2 g/L carboxymethyl chitosan, which was decreased by 12.96% and increased by 15.45% and 22.53%, respectively, compared with the control. Therefore, the application of a carboxymethyl chitosan solution may promote the growth, enhance the stress resistance, and alter the nutrient uptake of P. davidiana seedlings, especially at 2 g/L carboxymethyl chitosan.