Complex perovskites with general formula A(B′_1/3B″_2/3)O₃and A(B′_1/2B″_1/2)O₃ have been investigated to analyse the structure of B-site long-range order(LOR) and the effect of ordered structure on microwave dielectric loss.Ordering plays an important role in the dielectric loss.The dielectric loss decreases with the degree of LOR increasing.Moreover,methods to improve the degree of ordering such as sintering and chemical composition are discussed.Increasing the sintering temperature,reannealing at lower temperture and decreacing the cooling rate can effectively improve the degree of LOR.Besides,cation doping could also promote the formation of B-site ordered structure.