Central composite face-centered design (CCF) and response surface methodology were used in the experiment to examine the combined effect of temperature (12-34℃) and salinity (0-26) on the Na⁺-K⁺-ATPase activity from the gill of tilapia juveniles (GIFT strain) (mean body length (4.3±0.105)cm and mean body weight (2.45±0.153)g).The results showed that:(1)The linear and quadratic effects of temperature and salinity on the Na⁺-K⁺-ATPase activity were highly significant (P<0.01),and the interactive effect between temperature and salinity was nonsignificant (P>0.05);(2)Using the response surface method, the Na⁺-K⁺-ATPase activity varied with increasing temperature and salinity in a curvilinear way; (3)The model equation of the enzyme activity towards temperature and salinity was established,with R²=0.9829 and Pred.R²=0.855 (P<0.01).The model equation could be practically used for forecasting the gill Na⁺-K⁺-ATPase activity in GIFT Nile tilapia juveniles;(4)Via applying statistical optimization of the response of interest,results showed that the optimal factor combination was 24.15℃/11.75, at which the minimum Na⁺-K⁺-ATPase activity, 0.62μmolPi·mg^-1pr·h^-1, was reached, with the desirability as high as 0.961. The Na⁺-K⁺-ATPase activity can be used as an indicator of growth of GIFT Nile tilapia juveniles. In general,It can be said that the environment in which the Na⁺-K⁺-ATPase activity is weaker is suitable for the tilapia juvenile growth,and in this case the metabolism of tilapia is more efficient,and the energy consumed for osmoregulation is smaller.