Abstract: Using the hybrid progeny of the second-cycle breeding population of Larix kaempferi（Lamb.）Carr as research subjects, this study measured seedling growth, leaf δ¹³C, δ¹⁵Nvalues, and carbon and nitrogen contents to analyze the differences and interrelationships in growth, water use efficiency, and nitrogen use efficiency among different hybrid combinations. The aim was to preliminarily screen elite new germplasms with fast growth and high water and nitrogen use efficiency, thereby providing material support for the high-quality development of forestry. The results showed that the average height and ground diameter of two-year-old seedlings were 100.7 cm and 8.9 mm, respectively. The mean values of leaf carbon content, nitrogen content, C/N ratio, δ¹³C value, and δ¹⁵N value were 46.06%, 2.31%, 20.17, 3.67‰, and -41.09‰, respectively. Significant or extremely significant differences were observed among different hybrid combinations in seedling height, ground diameter, leaf N content, C/N ratio, and δ¹⁵N value, while differences in leaf C content and δ¹³C value were not significant. Leaf N content and δ¹⁵N value showed weak negative correlations with δ¹³C value, but the correlations were not significant. The correlations of leaf N content, δ¹³C value, and δ¹⁵N value with two-year-old seedling height and ground diameter were also not significant. Using two-year-old seedling height, ground diameter, and δ¹⁵N value as selection indicators, a comprehensive membership function evaluation method was applied, and two superior hybrid combinations (51-5-5 × 24 and 26 × 33) were selected, , which possess both relatively fast growth and high nitrogen use efficiency.