The utility model relates to a device for treating small-scale chromate waste water, in particular to a small device capable of automatically adjusting PH for treating chromate waste water through oxido-reduction and activated carbon, which comprises a water inlet pipe, an oxido-reduction reaction area, an adsorption area, a water outlet area, a chromic slag discharge pipe, an acid-base and reducing agent adding pipe and a drainpipe, wherein the water inlet pipe is arranged at the top end of a reaction device; the water inlet pipe is connected with the oxidation-reduction reaction area; the adsorption area is arranged on the outer layer of the oxido-reduction reaction area; the acid-base and reducing agent adding pipe, a stirrer and a PH detector are arranged at the top of a reactor; the chromic slag discharge pipe is arranged at the bottom of the oxido-reduction reaction area; the adsorption area is communicated with the oxido-reduction reaction area through a valve; the valve is arranged at the bottom of the adsorption area; an active carbon column is arranged in the adsorption area; the water outlet area is arranged at the outer part of the adsorption area; a water outlet pipe is arranged at the bottom of the water outlet area. The chromate waste water flows through the oxido-reduction area and the adsorption area and then is drained through the water outlet pipe, so that chromium ions in the chromate waste water can be effectively removed.