Synthesis of diaryl ether in water phase is characterized by taking aryl halogenide and phenol as raw material, taking water as solvent, auxiliarily heating by micro-wave, taking carbonate, fluoride, borate and hydroxide of alkali metal or alkaline earth metal as alkali, and C-O coupling reacting under transition metal catalyzing condition or without transition metal catalyzing condition, with ligand or without ligand, with surface activator or without surface activator. It achieves short reacting time, simple operation, easy separation and good reacting environment.