The microstructure evolution and mechanical properties of a T8-aged Al-Cu-Li alloy with increased pre-deformation (0-15%) were investigated, revealing the microstructure-strength relationship and the intrinsic strengthening mechanism. The results show that increasing the pre-deformation levels remarkably improves the strength of the alloy but deteriorates its ductility. Dislocations introduced by pre-deformation effectively suppress the formation of Guinier-Preston (GP) zones and provide more nucleation sites for T1 precipitates. This leads to more intensive and finer T1 precipitates in the samples with higher pre-deformation levels. Simultaneously, the enhanced precipitation of T1 precipitates and inhibited formation of GP zones cause the decreases in number and sizes of θ′ precipitates. The quantitative descriptions of the strength contributions from different strengthening mechanisms reveal that strengthening contributions from T1 and θ′ precipitates decrease with increasing pre-deformation. The reduced diameters of T1 precipitates are primarily responsible for their weakened strengthening effects. Therefore, the improved strength of the T8-aged Al-Cu-Li alloy is mainly attributed to the stronger strain hardening from the increased pre-deformation levels.