Ecological stoichiometry theory is an important tool that can be used to explore the law of substance cycling and the distribution patterns of nutrient elements. Carbon (C), nitrogen (N), and phosphorus (P) play an important role in regulating plant growth and various physiological functions. In recent years, some studies have reported that Larix principis-rupprechtii, which was introduced into Shaanxi Province in 1958, grew well during its initial stage, but as its age increased, the growth potential fell and soil fertility decreased. There has been a global trend towards forest ecosystem restoration and reconstruction. Therefore, we chose to study the Larix principis-rupprechtii plantation in the Qinling Mountains that contained trees with three different stand ages. These were 7 years old (7a), 12 years old (12a), and 22 years old (22a). The contents and mass ratios of the C, N, and P elements in the soil and leaves were investigated. The results showed that an increase in soil depth led to a decrease in soil C, N, and P contents for each growth stage. The soil C and P contents were different for the three stand ages. The soil C and P contents of 7a and 12a were significantly higher than those for 22a. In contrast, there was no significant difference in soil N between the stand ages. The soil C:P and N:P mass ratios for 22a were significantly higher than those for 7a and 12a, which indicated that P limited the development of Larix principis-rupprechtii as the stand age increased. There were no significant differences between soil C:N mass ratios for different stand ages. There were large significant differences in leaf N and P among the stand ages, but leaf C showed a different trend. The leaf N and P contents were highest during middle age. The leaf C:N and C:P mass ratios represent plant C assimilation ability to a certain extent. Therefore, these indexes could reflect nutrient utilization efficiency and the growth rate of plants. In this study, the leaf C:N and C:P mass ratios for 22a significantly decreased compared to the other stand ages, which showed that the N and P utilization efficiencies decreased as the stand age rose. The leaf N:P ratio varied from 6.8 to 9.3 for the three stand ages, which indicated that N was the main factor limiting the growth of young and middle aged Larix principis-rupprechtii stands. The C content and C:N mass ratio in the soil were positively correlated with the C content and the C:N mass ratio in leaves. However, the relationship between the soil and leaf P and C:P mass ratio was negatively correlated. The soil N and N:P mass ratio showed no significant correlation with leaf N and the N:P mass ratio. It is known that there is a close relationship between soil and leaf C, N, P and mass ratios. The negative relationship between soil P and leaf P showed that with low soil P, the middle aged plantation mainly supported growth through the reabsorption of plant nutrients rather than through the absorption of soil nutrients. Based on a comprehensive analysis of a number of factors, we conclude that N and P fertilizer should be applied to Larix principis-rupprechtii plantations. This is especially important during the middle growth phase. These fertilizer applications will help meet the nutritional needs of Larix principis-rupprechtii plantations and improve plantation productivity.