The small spacing tunnel is a kind of tunnel structural style which situates between ordinary tunnel and double-arch tunnel. It has attracted great attention due to its unique merit. This paper takes Xiamen Airport highway tunnel as an example, considering four different construction steps during small spacing tunnel construction. Author applied MIDAS-GTS software to carry on numerical simulation, the influences of excavating orders of four different construction steps about stratum distortion and stable situation of middle rock pillar are analyzed. The analytical results indicate that construction Step 2 and construction Step 4 can suit actual situation of this project.