(Pb,Sr)TiO₃ (PST) is a typical nonlinear dielectric material with its permittivity tunable under DC bias. In this context, randomly oriented and (100) oriented PST thin films have been prepared by the sol–gel method. A dipole azimuth dependent behavior is exhibited in the PST thin film through investigation of dielectric permittivity and tunability. Using the built dipole azimuth model, the dielectric tunability is recognized as rotation of the dipole under a DC electric field and is increased to the highest value with the polarization perpendicular to the DC electric field. The (100) oriented dipole has supplied therefore much higher tunability because of its easy rotation under a vertical electric field than that for a randomly oriented one. This work reveals the contribution of the dipoles to dielectric tunability, representing an important step toward exhibiting a tunable mechanism and designing highly tunable devices.