The hysteresis loop equation of PbZr0.4Ti0.6O3/SrTiO3 hetero-junction was constructed by the modified Landau-Devonshire thermody-namic model, and the analytical functions of remanent polarization intensity Pr, coercive electric field Ec and effective energy storage density Wrecwith respect to the thin film thickness h of PbZr0.4Ti0.6O3 were obtained, respectively, and then the effects of the thickness of the PbZr0.4Ti0.6O3 thin films on ferroelectric properties and ferroelectric energy storage properties were investigated. The results show that Pr, Ec and Wrec all increase nonlinearly with the increase of PbZr0.4Ti0.6O3 film thickness h, and reach saturation values of 75.3 μC·cm-2, 2 240.7 kV·cm-1 and 9.0 J·cm-3 when the thickness h is 57.0 nm, 64.2 nm and 65.8 nm, respectively, the energy storage conversion efficiency η, however, decreases nonlinearly with the increase of h, reaching a stable value of 4.79% when h is close to 52.6 nm. In addition, both W′rec(h) and η′(h), the instantaneous relative rates of change, decrease with the increase of h, when h is less than 2.4 nm, η′(h) is greater than W′rec(h), when h is greater than 2.4 nm, η′(h) is less than W′rec(h), and η′(h)/W′rec(h) tends to a stable value of 0.65 as h is close to 50.0 nm.