With the continuing deposition of atmospheric N and wide application of P fertilizer, N and P have become a major factor affecting the ecosystem C balance. Fine root morphological characteristics, such as the root length, surface area, volume, and tips, play a critical role in many functions, including nutrient absorption. Global N deposition and P addition induce changes in root morphology. Seedling density is an important factor affecting root morphology because of the enhanced resource competition among high density seedlings, which reflects the allocation ratio of photosynthetic C in the roots, and ultimately affects the overall plant C allocation balance. Understanding the effects of N and P additions and planting density on the fine root morphology is important to be able to improve fine root health. However, knowledge regarding the effects of N and P additions on the root morphology is limited, and it is still unclear how N and P additions and seedling density alter the fine root morphology of Cinnamomum camphora seedlings. In this study, the root morphology of C. camphora seedlings planted at different densities was evaluated, along with the root length, surface area, volume, and tips, in order to reveal the effects of N and P additions and plant density on the fine root morphological characteristics of this species. One-year-old C. camphora seedlings were used as test materials, and NH₄Cl and NaH₂PO₄·2H₂O were selected to simulate N deposition and P addition, respectively. N and P additions were performed with four different levels of treatment (control, N, P, and N+P), and seedlings were planted at four different densities (10, 20, 40, and 80 seedlings/m²). The results showed that the N, P, and N+P treatments increased the root length, surface area, volume, and tips of seedlings compared to those of the control treatment. The effect of N addition on root morphology was stronger than that of P addition under low planting densities. The N+P treatment had the greatest effect on the fine root morphology at densities of 10, 20, and 40 seedlings/m², while there was no significant difference in the effect of each treatment at 80 seedlings/m². With increased planting density, the length, surface area, volume, and tips of the seedling roots tended to decrease. The effects of different densities or treatments on the fine root length, surface area, volume, and tips of the seedlings were significantly different, but the interactive effect of density and N and P additions on the fine root morphology of the seedlings was not significant.