The lining thickness of rifled composite barrel recoilless gun involves lightweight of gun barrel and fatigue life. The research on the relationship between the lining thickness and fatigue life of this kind of gun is relatively few. Aiming at this problem, the numerical simulation of finite element software ls-dyna and the local stress-strain method were carried out. The effects of gun belt engraving and internal pressure load on the initiation life of fatigue crack of rifled composite barrel with different thickness of liner and different composite layers were studied. The calculation results show that increasing the thickness of the lining can effectively reduce the local maximum strain, and the high grade carbon fiber is more suitable for the weight reduction of the light weight recoilless gun.