The growth and physiology of Chlorella pyrenoidesa were studied by using Gynostemma pentaphyllum (Thunb.) Makino as the allelopathic material to study the different concentrations of G. pentaphyllum extract (0, 5, 10, 25, 50g/L). The results showed that the inhibitory effect on the growth of C. pyrenoidesa increased with the increase of the concentration of extract. And the maximum inhibition rate was 79.41%. The content of chlorophyll a in the cells treated with neutrophils was lower than that of the control group, and photosynthesis was affected. In order to inhibit the growth of C. pyrenoidesa, the cell membrane permeability (absorbance OD264) of the treatment group was significantly higher than that of the control group, which meant the cell membrane permeability increased with the increase of the concentration of the extract. At high concentration, OD260 and OD280 were significantly higher than the control group and increased with time. It proved that the permeability of the cell membrane was increased with the extension of time, and more soluble proteins and nucleic acid were infiltrate out of the cell. The experimental results indicated that inhibition was enhanced with the increase of the concentration, and its mechanism of action was to promote chlorophyll decomposition and increase cell membrane permeability as well as promote soluble protein to infiltrate into the cell, to increase the content of nucleic acid in order to damage to the structure of algal cells, metabolic dysfunction, and thereby achieve allelopathic inhibition of algae.