The functions of terrestrial ecosystems can be influenced by anthropogenic disturbances and global climate change, such as nitrogen (N) deposition and application of phosphorus (P) fertilizer. Atmospheric N compounds have increased sharply due to fossil fuel combustion, fertilizer use, and livestock husbandry development, which caused the atmospheric N deposition to increase. China has become the third largest N deposition area in the world followed by the United States and Europe. With further development of the economy, N deposition will be increasingly serious in China, especially in the developed southern China. An excess of N deposition can cause forest ecosystem N saturation, soil acidification, phosphorus limitation in the forest ecosystems. The acidic soils suffer from severe phosphorus deficiency in southern China. Thus P fertilizer is often applied in forestry production. But there are few reports on the effect of P addition or N+P addition on forest soils. The soil chemical properties were also influenced by N deposition and P fertilizer in forest ecosystem. Planting density can affect soil fertility by tree growth, completion of soil resource, and nutrient return from litter and root secretion. However, the responses of soil chemical properties to the N and P additions and planting density remain unclear. To date, no studies focused on the interactive effects of N and P additions and planting density on soil chemical properties in the southern China. The effects of N and P additions on soil chemical property were investigated in different densities of Cinnamomum camphora seedlings in order to provide a basis for the forest soil nutrient management. The study was conducted from June to September in 2017 using one-year-old C. camphora seedlings as test materials. We selected NH₄Cl and NaH₂PO₄·2H₂O to simulate atmospheric N and P additions with four treatments including CK (without nutrient added), N (40 g NH₄Cl m^-2 a^-1), P (20 g NaH₂PO₄·2H₂O m^-2 a^-1), and N+P (40 g NH₄Cl m^-2 a^-1 + 20 g NaH₂PO₄·2H₂O m^-2 a^-1). The seedling density was set at 4 levels (10, 20, 40, and 80 seedlings/m²). The results showed that in all density seedlings, N and N+P treatments significantly decreased soil pH, whereas soil organic matter and alkaline N treated with N, P, and N+P treatments changed irregularly. At the same time, soil total P content treated with P and available P content treated with P and N+P increased, and soil total K treated with N+P and available K content treated with N, P, and N+P decreased. The soil total N content treated with P was higher than that of N and N+P treatments in the density 10, 20, and 40 seedings·m^-2, whereas it was lower than other density seedlings in the density 80 seedings/m². The soil pH and the contents of total P, available P, total K, and available K treated with different fertiliser treatments increased with increasing seedling density. The content of soil organic matter treated with N or P decreased with increasing seedling density. The soil alkaline N treated with different fertiliser treatments changed irregularly. The interactive effects of density and N and P additions on soil organic matter, alkaline N and available K of seedlings were significant.