(1−x)Pb(Mg1/3Nb2/3)-xPbTiO3 (PMN-xPT) ceramics with x ranging from 0.1 to 0.3 were synthesized by solid-state reaction method. X-ray diffraction, dielectric and ferroelectric property characterizations were systematically investigated. As x rises, the PMN-xPT transitions from a cubic to a rhombohedral phase, resulting in an enhancement in ferroelectricity. Our findings show that the electrostrain and longitudinal electrostrictive coefficient Q33 both increase and then decrease within a critical region located between the depolarization temperature TFR and Tm (corresponding to the maximum permittivity), demonstrating strong temperature-dependent characteristics. In x = 0.2, the maximum Q33 of 0.0361 m4/C2 is obtained, and a phase diagram of studied system is built. Our findings not only shed light on the phase evolution in this system but also reveal a strong temperature-dependent electrostrictive effect that can be used to improve electrostrains in PMN-based solid solutions if the critical region can be regulated to a suitable temperature region using engineering strategies.