Stem cells have differentiation and regulatory functions. Here, we discuss the effect of cell culture density on stem cell proliferate, adipogenesis and regulation ability. To investigate the effect of the initial culture density of human periodontal ligament stem cells (hPDLSC) on the adipogenic differentiation of autologous cells. We found that the proliferation rate of hPDLSC increased with the initial cell densities (0.5~8 × 10 ⁴ cells/cm ²) increase. After adipogenic differentiation induced by different initial cell densities of hPDLSC, we found that the mean adipose concentration and the expression levels of lipoprotein lipase (LPL), CCAAT/enhancer binding protein α (CEBP-α) and peroxisome proliferator-activated receptor γ (PPAR-γ) genes all increased with increasing cell density. To investigate the regulatory role of hPDLSCs on the adipogenic differentiation of other cells, we used secreted exosomes derived from hPDLSCs cultured at different initial cell densities of 50 μg/mL to induce the adipogenic differentiation of human bone marrow stromal cells (hBMSC). We also found that the mean adipose concentration and the expression of LPL, CEBP-α and PPARγ genes increased with increasing cell density, the optimal culture density was 8 × 10 ⁴ cells/cm ². This provides a laboratory research basis for the application of adipogenic differentiation of stem cells.