In order to study the effects of light color and photoperiod on the growth and physiology of Salmo salar during smoltification, 3 photoperiods and 3 light source colors were designed by single factor analysis. Under the condition of red light, 24 h full on (24L: 0D) (full light), 24 h full off (0L: 24D) (no light) and 12 h on and 12 h off (12L:12D) (half light) were set, and under the condition of half light, red light, white light and blue light were set. The test cycle was four months, aiming at measuring the growth performance and serum biochemical indexes of Salmo salar. The results showed that under the condition of half light, the daily gain and the specific growth rate of Salmo salar were significantly higher than those under the condition of no light (P<0.05), while the bait coefficient was significantly lower than that in the other two groups (P<0.05). Light source color had significant influence on the growth of Salmo salar during smoltification (P<0.05). When the red light was used, the daily gain of Salmo salar was the highest, followed by that of white light group, and the lowest by that of blue light group, while the bait coefficient showed the opposite pattern. The salinity tolerance test showed that the mortality rate of the half light group was 10%, significantly lower than that of the other two groups (P<0.05), the mortality rate of red light group was about 10%, significantly lower than that of the white and blue light group (P<0.05). The analysis of serum indexes showed that the contents of sodium and chloride ions in the half light group were lower than those in the other two groups, suggesting that Salmo salar in this group had the ability of osmotic pressure regulation in seawater. In conclusion, red half light is suitable for aquaculture of Salmo salar during smoltification.