The Larix gmelinii forest is an important carbon sink in northern forests and also a dominant community type in the Daxing'anling Mts. Studying its species composition and spatial structure on aboveground biomass and soil nutrients can provide theoretical basis for the enhancement and scientific management of carbon sinks in northern forests in China. This study set permanent plots of Larix gmelinii forest in Dobukur National Nature Reserve as the research target, calculated the spatial structure characteristic index, species diversity index, and woody plant biomass of the forest stand, measured the organic carbon content, total nitrogen content, and total phosphorus content of 0-20 cm and 20-40 cm soil layers, and combined correlation analysis, redundancy ranking, and variation partitioning analyses to reveal the effects of tree diversity and forest spatial structure on tree biomass and soil nutrients. The results showed that: (1) Storey differentiation was significantly positively correlated with biomass, while uniform angle index and diameter difference index were significantly negatively correlated with biomass (p<0.05). The correlation between tree diversity index and biomass is not significant. (2) Species mingling was significantly positively correlated with organic carbon content in the 0-20 cm soils, but not significantly correlated with the 20-40 cm soil layer. The woody plant richness, Shannon-Wiener index, and Simpson index were significantly positively correlated with the organic carbon content in the 0-20 cm soils, while the evenness index was significantly negatively correlated with the organic carbon content in the 0-20 cm soils, but not significantly correlated with the 20-40 cm soil layer. (3) The biomass of woody plants was affected by stand spatial structure characteristics, and soil nutrients were mainly affected by tree species diversity, with an explanatory rate 5.8 times higher than the spatial structure characteristics of forest stands. (4) Redundancy analysis showed that the higher the richness of tree species, the higher the soil carbon, nitrogen, and phosphorus content. In summary, comprehensive management measures that adjust the spatial structure of forest stands can increase forest biomass, while emphasizing the protection of species diversity can improve the overall level of soil nutrients.