In this paper,the characteristics stability and the cultivation applicability of the improved strain(T-17)of Pyropia yezonensis were evaluated according to the results of laboratory cultivation and pilot cultivation in mariculture farm.The results showed that:in comparison with the wild-type strain(WT)of Pyropia yezonensis,the blades of the T-17 strain have obvious advantages in growth rates,maximum photochemical efficiency,contents of main photosynthetic pigments,blade thicknesses and yields of pilot cultivation.When the blades after being cultured at 18℃ for 50 days were cultured at 18,22 and 24℃ for another 35 days,the absolute growth rates of the blades of T-17 strain were 17.71,15.81 and 33 times higher than those of the WT strain,respectively;the specific growth rates of the T-17 strain were 4.59,4.38 and 9.15 times higher than those of the WT strain,respectively;the maximum photochemical efficiency(Fv/Fm)of the T-17 strain were 1.17,1.29 and 1.58 times higher than those of the WT strain,respectively.The gametophytic blades of the WT strain turned deeply dark,curly hardened and began to decay when the blades of the WT were cultured at 22℃ for 25 days,24℃ for 15 days and 25℃ for 10 days,respectively,while the blades of the T-17 did not harden,did not decay and grew well in the same culture conditions and were cultured for the same period.When the blades were cultured at 18℃ for 65 days,the contents of Chl.a,and phycobiliprotein(PE+PC)of the T-17 strain were 1.45 and 1.54 times higher than those of the WT strain.The mean blade thickness of the T-17 strain was less than the WT strain by 26.4%.The releasing number of conchospores from T-17 has no significant difference with the WT strain.The blades were collected and studied from the first harvest to the fourth harvest in the pilot cultivation.It was found that the fresh yield of the T-17 strain of the total amount of harvests in the first four times increased by 16.3% compared with traditional cultivar(the wild-type,Wt),the maximum photochemical efficiency(Fv/Fm)of the blades of the T-17 strain were 1.06,1.12,1.17 and 1.27 times higher than that of the Wt strain,respectively;the Chl.a contents in the blades of T-17 strain were 1.41,1.49,1.52 and 1.91 times higher than that of the Wt strain,respectively;the phycobiliprotein contents in the blades of the T-17 strain were 1.94,2.04,2.03 and 2.34 times higher than that of the Wt strain,respectively.Compared with the wild-type strain,the T-17 strain had higher yield,stronger resistance to high-temperature and higher quality,and good stability of the characteristics.This strain has probably great potential to be applied in commercial cultivation.