Inequivalent La3+ is firstly utilized to modify the microwave dielectric properties in SrTiO3 ceramic system. For the general composition of Sr1-xLa2x/3TiO3 (0 <= x <= 1), the effects of La3+ introduction on the phase transition and structural changes are systematically investigated. The correlation between A-site ordering degree and dielectric loss in microwave range is established, and the temperature coefficient of resonant frequency is also dramatically improved. When x = 0.945, excellent dielectric properties of epsilon(r) similar to 89.3, Qf similar to 15243 GHz (@ 4.3 GHz) and tau(f) similar to 160 ppm/degrees C are obtained, making it potential to meet the application requirements of 5G technologies.