In order to study influencing factors of fatigue cracking of the asphalt layer of tunnel semi-rigid base asphalt pavement, the fatigue cracking of the asphalt layer was researched by establishing a finite element model of tunnel semi-rigid base asphalt pavement. The results show that maximum tensile strain of the asphalt pavement inside is significantly bigger than that of the asphalt pavement bottom, which causes that fatigue life of the asphalt pavement inside is far shorter than that of the asphalt pavement bottom. The sensitivity of influencing factors of fatigue cracking life of the asphalt layer bottom is ranked as follows: the modulus of the base layer＞ the modulus of the surface layer ≈ the thickness of the surface layer＞ the thickness of the base layer.The larger the base layer modulus is, the thicker the base layer thickness is and the smaller the asphalt surface layer modulus is, the more favorable for the fatigue cracking life of the asphalt layer it is.