Abstract: This study was carried out at Guanshanyuan, Songyang County,Zhejiang Province. Density and biomass dynamics as well as their interrelationship for Pinus taiwanensis populations are described. Pinus taiwanensis is one of the pioneer species in forest succession in this region. The analysis of the population dynamics of Pinus taiwanensis throughout the successional process revealed the following three phases.Until ca. 9–10 years after Pinus taiwanensis invades the stands, the density of population is increased by the recruitments along with increase of the mean tree weight and population biomass (phase Ⅰ).Thereafter, the population is in full density state, the biomass of population and the mean tree weight increases exponentially, while the density of population is decreased drastically by the self-thinning and the invasion of other broad-leaved trees (phase Ⅱ). The –3/2 power law of natural thinning is applicable to the population in this phase. When the broad-leaved trees reach the canopy of forest, although the mean tree weight increases slowly, the density and biomass of Pinus taiwanensis population decreases gradually (phase Ⅲ) until the population senesces and retreats from the successional series completely. At some special habitats such as rocky steep slopes and ridges, however, Pinus taiwanensis population can form such an edaphic climax community that the density and biomass of population and the mean tree weight can be in a stable state for quite long period(phase Ⅲ).