The annealing effects on Pb0.97La0.03Sc0.45Ta0.45Ti0.1O3(PLSTT) ceramics prepared by the solid-state reaction method are systemically investigated using experimental and theoretical techniques. Comprehensive studies are performed on the PLSTT samples by varying annealing time (AT) fromt(=0, 10, 20, 30, 40, 50 and 60) h. The properties involving ferroelectric polarization (FP), electrocaloric (EC) effect, energy harvesting performance (EHP) and energy storage performance (ESP) are reported, compared and contrasted. All these features are seen to gradually improve with the increase in AT, and they all reach the climaxed-shaped values and then decrease by further increasing the AT. Fort= 40 h, the maximum FP (23.2 µC/cm2) is attained at an electric field of 50 kV/cm, while the high EHP effects (0.297 J/cm3) and positive EC are achieved (for ΔT~0.92 K and ΔS~0.92 J/(K·kg)) at 45 kV/cm. The EHP value of the PLSTT ceramics increased by 21.7% while the polarization value was enhanced by 33.3%. Att= 30 h, the ceramics have attained the best ESP value of 0.468 J/cm3with an energy loss of 0.05 J/cm3. We strongly believe that the AT plays a crucial role in the optimization of different traits of the PLSTT ceramics.