Azo dye is a kind of synthetic dye containing azo group (Ar-N N-Ar). In this paper, an efficient process intensification for the continuous synthesis of azo dye is developed by using a microreactor system. Firstly, the reaction conditions of azo-coupling reaction were optimized and a microreactor was utilized as the mixing and reacting unit. 1- (4- sulfonicphenyl) -3- methyl -5- pyrazolone was the coupling component and aniline was the diazo component. The results show that the yield of azo-coupling reaction was higher than 96% under optimized condition. Then, the reaction conditions of diazotization were optimized by orthogonal experiments in a microreactor system. Combined with the optimization of azo-coupling reaction conditions, the optimal conditions of continuous-flow synthesis of azo dyes in microreactor as were determined. Then, four model azo dyes were synthesized by the continuous method in microreactors. The yields of No. 1, No. 2 and No. 4 azo dyes were above 96% and the yield of No. 3 azo dye was above 90%. Finally, the commercial azo dyes were synthesized continuously in microreactors and the yields were above 94%. The continuous-flow synthesis of azo dyes in a microreactor system has great potential in industrial applications.