I heard they are making another 阿凡达 sieries. Is it true?

yes! the plot is that it's 70 years after aang defeated the 火, 消防 lord and there is a new 阿凡达 a southren water tribe water bender Korra! she has already mastered water earth and 火, 消防 so now she is going to the melting pot city filled with non benders and benders to learn air from aangs son Tenzin! but in the city an anti bending group is rising to get rid of benders! so now korra will have to deafeat them ! it premires august 2011 =) here is a pic to prove it ! =)

It is. The Legand of Korra. Exciting, ain't it?