For clarifying the physiological and ecological adaptability of leaves of Sargassum thunbergii, the photosynthesis and respiration were investigated by using liquid-phase oxygen measurement system. The major results included two aspects: 1) The differences of maximal net photosynthetic rate (Pnmax), saturation irradiance (Isat), light compensation point (Ic), initial quantum yield α, dark respiration rate (Rd), pigment content, specific leaf area and microstructure of heteromorphism leaf (broad leaf, narrow leaf, pneumathode) were analyzed to reveal the probable reason about the change of leaf shape of S. thunbergii. 2) Effects of different temperatures and different salinities stress on Pn and Rd of broad leaves of newborn branch of S. thunbergii were researched. The preliminary analysis of the newborn branch about resistance physiology could provide reference for the artificial cultivation of S. thunbergii based on vegetative reproduction. The results were shown as follows: The optimum temperature for growth of newborn branch is 15-24 ℃ under the experimental condition in this paper. Pn had significant reduction when temperature was 5 ℃ or higher than 30 ℃ and Rd was significantly affected by low temperature (10 ℃ or below) or high temperature (higher than 30 ℃) stress for one hour treatment. However, Pn or Rd of low temperature stress groups could nearly recover to normal level after 24 h under standard culture condition. Short-term high or low salinity tests, especially salinity 0 and salinity 60 stress, had significant influence on Pn of broad leaves. However, Pn of salinity 0 group could recover to normal level after a 24 h recovery period, but Pn could not recover after exposure to salinity 60 for 9 h. During the whole stress process, Rd of salinity 40 and salinity 50 treatments both showed high value. And salinity 0 and salinity 60 stress both had significant influence on Rd. However, Rd could recover to normal level after a 24 h recovery period after exposure to different salinities for 9 h.