The effects of different heat treatment on the tensile properties and microstructure of a 2050 Al-Li alloy sheet were investigated through mechanical testing and TEM. The result indicate that the mainly strengthening precipitates of 2050 Al-Li alloy are T1 and θ′ phases. The aging precipitation characteristic is different upon T6(175℃) and T8(6% pre-deformation+155℃)aging. Compare to T6 aging, the pre-deformation before T8 aging increases the density of T1 and θ′ precipitates, reducing the size and the corresponding strength and elongation are improved. At T8 peak aging state, the σb、σ0.2、δ reached of 531 MPa、488 MPa、11.4%，respectively. The scope of 2% to 10% pre-deformation before T8 aging can promote T1 phase nucleation, the 2% to 6% pre-deformation can promote θ′ phase nucleation. Large deformation (such as 10%) has little effect on further nucleation of θ′ phase, but significantly inhibit the θ′ phase grew up.