Abstract: The results of propagation coefficient test showed that salt-tolerant threshold of back-crossed azolla was 0.8% NaCl concentration. The physiological and biochemical indexes were mea-sured under salt stress condition. The content of proline was accumulated, and the plasmalemma permeability(PP)and malonidialdehyde(MDA)content increased. The measurement on cell pro-tective enzymes showed that SOD and POD activities increased with the increase of salt concentra-tions; CAT reacted sensitively to salt, its activity increased rapidly under the low salt stress. The analysis on esterase isoenzyme spectra in different salt concentrations showed that the salt stress induced the relevant genes to express new bands and inhibited some original bands. It was suggest-ed that the saline harmness in azolla might be as a result of lipid reoxidation and osmotic stress.