Abstract: By using hybrid azolla Rongping No. 1 as paternal,A. microphylla which was the maternal plant of Rongping No. 1 as maternal material for combination,a back-crossed hybrid azolla,MH3-1 has been achieved.It was proved to be a real hybrid azolla by the identification of esterase zymogra-phy.Its heat-tolerant capacity is higher than paret plants and other tested azolla strains;the salt-toler-ant capacity showed the same tendency. Furthermore,it gets good quality,high multiplying speed,and suitable to be cultured in paddy field in late rice season,and utilized for the development of coastal saline soil.The analysed results showed that,MH3-1 increased significantly the activities of its intra-cellular enzymes,including peroxidase and super-oxide dismutase to compare with other azolla strains,which is considered as the physiological basis of cell membrane to protect the back-crossed azolla from the harmness of salt stress.