Nostoc flagelliforme was cultured in BG11, with different concentrations (0, 0.1, 0.2,0.4 mol . 1, L-1) of NaCl. The results indicated the photosynthetic rate and chlorophyll fluorescence increased firstly and then reduced following the increase of concentrations of NaCl. N. flagelliforme had the maximal photosynthetic rate and chlorophyll fluorescence at 0.1 mol . L-1 NaCl. The results show(,(] that the cultivated N. flagelliforme had the tolerance to a certain concentrations of NaCl. N.. flagelliforme cultivated in Will. and added 0.4 mol . L-1 NaCl was the control. In the experiment of BG11 and addition of 0.1 mol . L-1 NaCl, the photosynthetic rate and chlorophyll fluorescence decreased slowly, the content of MDA and proline were lower,the content of carotenoids increased compared with those in control. The results implied that the addition of nitrate could reduce the effect of salt stress to the cultivated N. flagelliforme and enhance its ability in resistance to salt stress.