This paper applies niche theory to survey the development strategies and competitive actions of Small-and medium-sized Enterprises(SMEs).It points out that SMEs should separate their niches from those of large enterprises initiatively， and then puts forward mini-niche strategy based on niche separation and deep-adaptation strategy which helps SMEs to consolidate their positions in mini-niches. It provides new ideas and methods for SMEs to survive and develop in the fierce market competition.