Abstract: Spatial and temporal variations of the soil-plant-atmosphere-continuum (SPAC) water potential gradient and sapwood flow velocity in Pinus tabulaeformis and related factors were measured using a thermal dissipation probe (TDP) and micro-weather station that kept a continuous record of solar radiation, air temperature, air humidity, wind speed and wind direction, rainfall, and soil temperature at the teaching and researching station of Beijing Forestry University in West Mountains of Beijing in April 15-24, 2001. The results showed that soil humidity declined in the top layer soil and declined only to a small extent in the deep layer soil. Following a simulated rain event of 47.77 mm, surface soil water potential increased abruptly and water potential in the mid-layer soil increased after 2 days later but decreased and approached that of the control gradually due to wood evapotranspiration. Compared to the large water fluctuation in the surface and mid-layer soil, diurnal water potential in deep soil had stable daily fluctuations. The water potential of the SPAC elements decreased gradually from the soil to air. The soil-leaf-air water potential gradient of the rain treatment increased to 1∶15∶90 as compared to 1∶5∶30 of the control. Water potential differences of the leaf-soil, air-leaf and air-soil also increased after watering. The daily water potential of the SPAC elements declined gradually after a long drought period and declined in the following order: air>leaf>soil. The lowest daily leaf water potential occurred at 14∶00 pm, 4 hours earlier than the soil. The lowest air water potential occurred at the same time. Air temperature was the dominant environmental factor affecting air and soil water potential, and relative humidity of the atmosphere and soil moisture were the most important factors affecting leaf water potential. There were significant correlations between the surface soil and leaf water potentials the surface soil and air water potentials both for the treatment and control. Daily sapwood flow velocity (SFV) fluctuated in accordance with variations in the water potential of the SPAC elements and meteorological factors. Significant correlations were found between SFupper and 50 cm deep soil water potential, wind speed, solar radiation intensity, air humidity and air temperature, SFlower and soil temperature between 10-50 cm, wind speed, air humidity and air temperature for control, SFupper and wind speed, solar radiation intensity, air humidity and air temperature, SFlower and soil temperature between 10-50 cm for watering treatment. Correlation coefficients between SFV and the water potential of the different SPAC elements decreased with watering.