The Qinling Mountains have some of the best sites for research on impact of climate change on forest growth in China. We selected two main forest types in the mountains, Pinus tabulaeformis and Pinus armandi forests, to explore relationships between net primary productivity (NPP) of the tree layer and climatic factors in order to understand response of the growth to climate change. Nine plots of P. tabulaeformis and fifteen plots of P. armandi forests were established at the Huoditang forest region in the Qinling Mountains. More than 20 cross increment cores were extracted from different trees at each plot. After being cross dated by the skeleton diagram method, tree ring widths of increment cores were measured with WINDENDRO tree ring system. Annual diameters of sample trees were calculated using tree ring widths. Regression equations between diameter at breast height (DBH) and height of P. tabulaeformis and P. armandi forests at the Huoditang forest region were used to estimate the annual biomass and NPP from 1973 to 2011. Then correlations were analyzed between NPP and climatic factors including monthly and seasonal temperature and precipitation. Multiple stepwise regression analysis was used to select the climatic factors with the most impact on the annual NPP of the two forest types. A relatively consistent dynamic trend was found in the biomass and NPP of the two stands. The biomass of P. tabulaeformis and P. armandi forests increased dramatically in the past 39 years from 15.32 t/hm² and 7.53 t/hm² to 175.97 t/hm² and 130.98 t/hm², respectively, and the mean annual NPP were 4.18 t hm^-2 a^-1 and 3.20 t hm^-2 a^-1 respectively. Higher biomass and NPP of the tree layers were found in P. tabulaeformis compared to P. armandi forests. No significant correlation was observed between the NPP and monthly and seasonal precipitation; in contrast the NPP was closely correlated with the monthly and seasonal temperature. Among the monthly temperature factors, the temperature in July of the previous year correlated positively with NPP for P. tabulaeformis and P. armandi forests. Also the temperature in the current July correlated with NPP in the same year in P. tabulaeformis forests. Among the seasonal temperature factors, a significant coefficient was observed between the NPP of P. tabulaeformis forests and the mean temperature from January to July. A significant coefficient was observed between the NPP of P. armandi forests and the mean temperature from May to July; higher coefficients were found between the NPP of and climatic factors in P. tabulaeformis forests than that in P. armandi ones. The difference in the biomass and productivity between two kinds of forest types are due to their different biological characteristics.