Pleioblastus pygmaeus (Miq.) Nakai, as a dwarf bamboo, providing a high ornamental value in landscaping. Furthermore its well-developed and intricate root system lends its use for soil consolidation and slope protection. A pot experiment was performed to study the impact of different light intensity on the growth characteristics of P. pygmaeus seedlings. The light intensity was controlled by punching circular holes with different diameters in center of the plates cover the pots. The illuminance percentages of the pore diameter area to the inner diameter area of the pot in each treatment were 1.29% (A), 5.16% (B), 11.62% (C), 20.66% (D), 32.28% (E), and 100% (F). The average illumination intensity under treatment A, B, C, D and E is 3.87%, 11.25%, 20.25%, 38.76% and 60.70% of control F (100% of full sunlight), respectively. The results showed that the light intensity is a key factor influencing P. pygmaeus seedlings’ growth and mortality. Seedlings died when light is lower than 38.76%. As light intensity decreased, the mortality increased and the number of culms and total rhizomes, leaf-, aboveground- and underground-biomass significantly decreased, and the gap between the treatments and control significantly increased over the nine month growing period. The generalized additive model (GAM) explained the influence of illuminance and investigation time and indicated a lower determination coefficient on culm height, culm diameter, total rhizome length and total rhizome diameter compared with number of culms, number of total rhizomes and biomass. The diameter of culms showed a decreasing trend during the experiment while their lengths increased even under A treatment (3.87% of full sunlight), suggesting that nonstructural carbohydrates stored prior to the experiment was used for culm height growth under light/carbon limitation. In the case of the leaves, their growth was significantly inhibited under low light intensity (3.87–60.70% of full sunlight) as they are the primary component of the plant's photosynthetic apparatus. As suppressed leaves could not independently provide enough carbon to the plant, P. pygmaeus seedlings adjust their plasticity to slow down rhizome growth, shoot emergence and biomass accumulation, eventually resulting in “Carbon starvation” and increased mortality. This study provides insights into how dwarf bamboos balance growth and survival under low light availability.