4-methoxy-3-halogenated biphenyl was synthesized from p-dimethoxybenzidine via diazotization at -5～0℃ and Sandmeyer reaction with Cuprous Bromide or Cuprous chloride at 90℃, Some factors affected the reaction，such as the mw material rate，the reaction time and the reaction temperature were also discussed. The structure of the product was confirmed by melting point, IR and 1H NMR .The results show that the total yield of 3-Chloro-4-methoxybiphenyl synthesized by this preparation procedure was 63% and 3-Bromo-4-methoxybiphenyl was 51%.