Abstract:Abstract: The effects of heat treatment on the tensile properties and fatigue crack propagation（FCP） behaviors of new Al-Cu-Li alloy were investigated. The microstructure and fracture morphology were observed and analyzed by OM, SEM and TEM. The results indicate that the new Al-Cu-Li alloy can obtain the best comprehensive properties under 540℃/1h solution treatment and （12?AaRT（5d） 145℃（20h））aging treatment condition, with σb =443Mpa，σ0.2 =397Mpa,δ=16.5%，da/dn=1.34*10-3mm/cycle（△K=30 Mpa*m1/2）. The two-step artificial aging can improve the resistance to crack propagation of the alloy by promoting the precipitation of the fine, dense and uniform T1(Al2CuLi) phase in the matrix, while the strength is also high; In T8 temper; the alloy will precipitate some relatively coarse T 1 phase ,θ′phase and a few S′phase which achieve the demand of the high strength ,while not satisfying the requirement of crack propagation resistance . In T3 temper ,the alloy has a poor strength with the few strengthening phase existed.