The invention discloses an arc reactor. A reactor main body comprises a water distribution region, a main reaction region, an auxiliary reaction region, a three-phase separation region and a precipitation region from bottom to top. The main reaction region is divided into a first reaction chamber and a second reaction chamber by a three-tube separator; the two reaction chambers control automatic gas stirring through respective gas-stirring control tubes; and the auxiliary reaction region is located above the main reaction region for further degrading the matrix carried by the gas on the main reaction region. The invention has the advantages as follows: (1) sewage can be effectively intercepted and the microbe in the reactor is maintained through the three-tube separator and the precipitation region; (2) the main reaction region is connected with the auxiliary reaction region in series to prevent the matrix from backmixing and improve the processing efficiency; (3) the mass transferring effect can be strengthened and the dead spaces of the reactor are reduced through respective gas stirring in two reaction chambers in the main reaction region; and (4) the matrix carried by short stream in the main reaction region can be complementally processed and the negative effect caused by the short stream is prevented by matching the heights of the main reaction region and the auxiliary reaction region.