Direct evidence of epiphytic algal effects on the photosynthetic function of submerged macrophytes is scarce. To obtain more reliable, quantitative data about this phenomenon, a laboratory experiment was carried out over 42 days in controlled conditions with the submerged macrophyte, Potamogeton crispus. It was based on a 2 x 3 factorial design with two epiphytic conditions (with bioconlrol and without) and three nutrition levels (mesotrophic t eutrophic, hypertrophic), to study on the epiphytic algae booming and the effect of epiphytic algae on the photosynthetic function of P. cripus in different nutrition levels. The result showed that enhanced availability of major nutritional elements like N and P promoted epiphytic algae booming growing, and with a production velocity of 0.16 Chi.a μg/cm²·d on leaves surface under eutrophic conditions (TN:lmg/L;TP:0.lmg/L). However, the booming growth of epiphytic algae was obstructed by biocontrol with Macrobrachium nipponense + Radiuauricularia, even in eutrophic conditions. Original position survey of leaves’ chlorophyll fluorescence parameters showed as follows. Epiphytic algae booming growing on leaves surfaces for 42 days resulted in leaves’ chlorophyll-a density declining by 25.2%, carotenoid density declining by 20.8%, effective quantum yield of PSII declining by 9.8%, electron transport rate (ETR) declining steadily, and photochemical quenching(qP) declining more than 60%. It can be concluded that the booming of epiphytic algae might have affected the growth of P. crispus. by altering the leaf density segments and photosynthetic function of P. crispus.