Using the method of space instead of time, Pinus massoniana plantations of 8, 18, 26 and 36 years old were selected as the research objects on plateau mountains, central part of Guizhou Province, and the content of soil organ carbon (SOC), total nitrogen (TN) and total phosphorus (TP) were determined in the four plantations to analyze the variation law and stoichiometric characteristics of nutrient contents at different development stages. The results showed that the average value of SOC, TN and TP in four P. massoniana plantations at the different ages were 12.24 g/kg, 1.94 g/kg and 0.35 g/kg, respectively, and the average value of C:N, C:P and N:P were 6.58, 38.70 and 13.65, respectively. The average ecological stoichiometric ratio of C:N:P was 39:6:1. Generally, the soil nutrient was insufficient in the four P. massoniana plantations. Soil SOC and TN of the four plantations decreased with the increasing of soil layer depth, but C:N increased, while the change rule of TP, C:P and N:P was not obvious. With the increasing of plantations age, content of SOC and TN and N:P decreased first and then increased, and TP decreased persistently. Meanwhile, C:N significantly decreased in the 36-year-old plantation, but there was no significant difference in other plantations. There was no obvious change rule for C:P. The correlation analysis showed that soil SOC and TN were the main factors regulating the soil ecological stoichiometric ratio of P. massoniana plantations. These results could provide important reference for illuminating soil nutrient cycling of P. massoniana plantations in plateau mountains.