Chlorophyll fluorescence technique can provide an accurate, quick, and non-destructive assessment of the efficiency of photochemical conversion. One of the most commonly used fluorescence parameters is the maximal quantum yield of photosystem Ⅱ (PSⅡ) (), which has been shown to be a sensitive indicator of photoinhibition. Moreover, other fluorescence parameters, such as the effective quantum yield of PSⅡ (yield), the relative electron transport rate (rETR), photochemical quenching (qP), non-photochemical quenching (NPQ), the initial slope of rapid light curve (), and the minimum saturating irradiance (I_k), are also important in investigating photosynthesis. As such, chlorophyll fluorescence has become an increasingly powerful tool and widely used technique to study photosynthesis in marine algae. Caulerpa lentillifera is a tropical macroalga that grows mainly in Okinawa, Malaysia, the Philippines, Vietnam, and other places. is a potential healthy food with high nutritional value that contains a variety of essential amino acids, vitamins, mineral elements, and unsaturated fatty acids. In addition, also contains caulerpenynes, polysaccharides, and other physiologically active substances. It has beneficial effects for type Ⅱ diabetes and cancer. belongs to the marine benthic green algae, which are very sensitive to high light intensity. Light intensity reportedly has a significant effect on the growth of , but the effect of different light intensities on the photosynthesis process of is still unknown. Therefore, there is a need to better understand the photosynthetic characteristics of by investigating the effects thereon of different light intensities. In this study, the chlorophyll fluorescence characteristics of were investigated with MINI-PAM chlorophyll fluorometer under the light intensities of 10 μmol/(m²·s), 120 μmol/(m²·s), and 360 μmol/(m²·s). From 10 μmol/(m²·s) to 360 μmol/(m²·s), the maximal quantum yield of PSⅡ, the effective quantum yield of PSⅡ, the relative electron transport rate, and the initial slope of rapid light curve of all decreased with increasing light intensities. The samples treated with light intensities of 120 μmol/(m²·s) and 360 μmol/(m²·s) had higher photochemical quenching and lower non-photochemical quenching than those treated with 10 μmol/(m²·s). The minimum saturating irradiance increased dramatically and the maximum relative electron transport rate decreased sharply in ·s), but both were significantly higher under the light intensity of 120 μmol/(m²·s) than that in samples exposed to the light intensity of 10 μmol/(m²·s) for 4 h and 8 h. The minimum saturating irradiance and the maximum relative electron transport rate was substantially lower in ·s) from 8 h to 12 h. These results suggest that is a kind of seaweed adapted to a low light intensity of 10 μmol/(m²·s), and that it could im-prove light tolerance in different ways under high light intensities of 120 μmol/(m²·s) and 360 μmol/(m²·s), but light intensity of 360 μmol/(m²·s) for up to 12 h could cause photo-oxidation and damage its photosynthetic structure.