As raw material, paminobenzene sulfonic acid, sodium nitrite and N,Ndimethylaniline is used to synthesize methyl orange by diazotization and coupling reaction. The traditional method for the synthesis of methyl orange, synthesis of methyl orange at room temperature and at room temperature in water phase medium are compared. The dosage of the reactant, reaction temperature, reaction time, pH value of the solution and the adjuvant effect are studied and the optimized condition for the syntheses is found out. The experimental results show that the reaction time of synthesis of methyl orange at room temperature in water phase medium is shortest, reaction temperature is easily controlled, the yield is highest, and the product purity is highest. The dosage of N,N dimethylaniline is 1.3mL, the reaction temperature is 20℃, the reaction time is 2h, pH value of the solution is 6, the adjuvant is ethanol or ether, under which the methyl orange yield is up to 87.09%. The method can be applied in industrial production for easy operation with less reagent and energy consumption.