The middle stratum is practically an aggregate of the class and group with middle social and economic status,whose economic,political and social status is placed between elite stratum and masses stratum.Enlarging middle stratum is the necessary requirement for constructing harmonious society.The middle stratum can be enlarged by using financial and taxation policy to develop education and science and technology,by encouraging the people to do pioneering work,by establishing reasonably social status change mechanism and so on,which play an important role in enlarging middle stratum to construct socialism harmonious society.