Combined sewage treatment system

The embodiment of the utility model provides a combined sewage treatment system. The combined sewage treatment system comprises an oxidation system and a biochemical system matched with the oxidation system, the oxidation system comprises an ozone generating device, an oxidation contact tank and a tail gas destroying device; the ozone generating device is arranged at the front end of the oxidation contact tank and is used for generating ozone gas; the oxidation contact tank is used for carrying out oxidation reaction on the sewage and ozone gas, and a first agent adding device for adding a first agent and adjusting the pH value of the sewage entering the oxidation contact tank to a first value is arranged at an inlet of the oxidation contact tank; a second agent adding device for adding a second agent and adjusting the pH value of the sewage to be discharged in the oxidation contact tank to a second value is arranged at the outlet, and the second value is greater than the first value; the tail gas destroying