Abstract: To explore effects of cloudy day on growth index of Penaeus vannamei and physiochemical characters of aquaculture water, the low light environment in cloudy day was simulated by adding black shade net to P. vannamei in the 1^st, 3^rd, 5^th, and 7^th week of the 7-week trial. The control group was exposed to daylight in the whole experimental period. The results revealed significant differences on pH, DO, Chl. a, \rmNH_4^ + -N, \rmNH_3 -N, \rmNO_2^ – -N, \rmNO_3^ – -N, \rmPO_4^3– -P between the shade group and the control group (P<0.05). Cloudy day simulation significantly reduced Chl. a level but significantly increased the concentration of \rmNH_4^ + -N and \rmPO_4^3– -P (P<0.01). Cloudy day simulation showed no signifi-cant change in the concentration of Chl. a, \rmNH_4^+-N and \rmPO_4^3– -P. Cloudy day simulation increased concentration of \rmNO_2^ – -N in the first 5 weeks, which was reversed at the 6^th and 7^th week. Cloudy day simulation also enhanced \rmNO_3^ – -N concentration for the whole time. These results suggest that NH₃-N and \rmNO_2^ – -N may inhibit the growth of P. vannamei. The algae could indirectly benefit the growth of P. vannamei. Cloudy day simulation inhibited algae from absorbing the toxic ions in aquaculture waters and deteriorated the growth and survival of P. vannamei.