It is a small chlorine dioxide multistage generator with simple operation, high conversion efficiency, high purity, multiple purposes and environmentally friendly chemical method. This chlorine dioxide generator is composed of tank reactor through the acid-resisting guide tube and water jet vacuum unit. The tank reactor is the two-stage or multistage reactor. The main reactor is equipped with the air distributor, and the side reactor is equipped with the balance tube, realizing more thorough reaction. The residual liquid after reaction can realize the up-to-standard discharge. The generated chlorine dioxide can prepare the water solution and the steady chlorine dioxide solution.