Abstract: In this study, the cyanobacterium Phormidium was grown under six different nutrient concentrations, ranging from standard AA medium to a 600× dilutions of that media. After incubation at 25 ℃ and 2000 lx for 8 months, the growth curve for each treatment was measured by direct counting of cell numbers. Additionally, the lytic cycle and mortality rate were determined by monitoring the lytic effect of the host cells using microscopy. The adsorption rate of cyanophage PP was measured using the centrifugation method, where the burst size and lytic cycle were confirmed by measuring the one-step growth curve. Results indicated that elevated TN and TP could significantly promote the growth of Phormidium. Statistical analysis showed that during the mid-log phase (day 6th) cell densities were significantly higher under high nutrient conditions. Additionally, the adsorption rate in standard AA medium was significantly higher than that in the other five dilution media. Although nutrient conditions did not affect mortalityrate significantly, the latent period and lytic cycle of cyanophage PP were obviously shortened. Moreover, the average burst size of cyanophage PP increased significantly with increasing the nutrient concentration. These results not only proved that high nutrient concentration could promote cyanophage infectivity, but also implied that cyanophage might play an important ecological role in adjusting the succession of algal populations in the progress of eutrophication.