The photoreactivation ratio of cyanophage PP in its wild host was studied. The results indicate that the photoreactivation ratio in wild host was significantly higher than those of cultured hosts (Phormidium foveolarum IU427 and Plectonema boryanum IU594）. Besides, the influences of ecological factors, including light quality, light intensity and water temperature, on the photoreaction ratio in wild host were also studied. The results indicate that the photoreactivation ratio was positively correlated with UV\|A intensity, visible light intensity and water temperature (P<0.05). Moreover, the photoreactivation ratio caused by visible light was significantly higher than that caused by UV\|A, and the photoreactivation ratio could approach its maximum when the visible light intensity reached 160μE?m-2?s-1. Our results suggest that visible light may be the dominant power for photoreactivation in shallow lakes, and the photoreactivation ability of wild host may be weakest in winter and strongest in autumn as far as the combined effect of water temperature and transparency was concerned.