Abstract: The process of developing the sieve cell of secondary phloem in Cunninghamia lanceolata (Lamb.) Hook. could be divided into two stages, i. e. radial expanding of the mother cell and orderly degradation of nuclei and organelle. After first stage, the sieve area began to form, and the wall became tiny thicken, but sill was primary cell wall. In the second stage, organelles degraded. The endoplasmic reticulum played a main role in the whole process. The vacuole membrane was not ruptured. The mature sieve cell plastid was starch. The P - protein was not found. The nuclear degradation was similar to program cell death.