This study aimed to understand the changes in spatial and temporal dynamics of water conservation in the process of stand improvement of Pinus massoniana, in order to improve the forest ecological service function. We analyzed the changes in stand water holding capacity between the control stand and improved stand using thinning intensities of approximately 20%, 35%, and 50%, in a 22-year-old P. massoniana forest of the Youxi Forest Farm in Fujian Province. The results showed that forest water conservation by stand improvement significantly increased with time (P < 0.05), and forest water conservation increased significantly with the increase in thinning intensity after 10 years. Water holding capacity of the soil layer accounted for 95.89%-97.18% of the stand water holding capacity. Water holding capacity of the 0-20cm and 20-40 cm soil layers was not significantly different between the control stand and improved stand during first five years of stand improvement (P > 0.05); however, after 10 years of stand improvement, water holding capacity of both 0-20 cm and 20-40 cm soil layers of the improved stand was significantly higher than the control stand (P < 0.05). Water holding capacity of the canopy, vegetation, and litter layers accounted for 2.82% (45.64 t/hm²)-4.11% (76.81 t/hm²) of the stand water holding capacity. In the canopy layer, water holding capacity of the improved stand was significantly higher than the control stand when stand improvement was > 10 years (P < 0.05); water holding capacity decreased with increasing thinning intensity. In contrast, in the vegetation layer, water holding capacity of the improved stand was significantly lower than that of the control stand when stand improvement was > 5 years (P < 0.05); water holding capacity decreased with increasing thinning intensity. In the litter layer, water holding capacity of the improved stand was significantly higher than that of the control stand when stand improvement was > 5 years (P < 0.05); water holding capacity increased with increasing thinning intensity. The water holding ratio of the canopy and litter layers increased significantly with time (P < 0.05), but the water holding ratio of the vegetation layer decreased significantly with time in the improved stand (P < 0.05). These results indicate that the stand water holding capacity changed dramatically in the early stage of the improved stand, and the water holding capacity decreased with increasing thinning intensity. Thus, the improved stand was more beneficial for water conservation over a longer period of time.