Police say an officer suffered concussion and facial cuts after a vicious attack near Turangi.
They say the 59-year-old was on highway patrol on Sunday afternoon, when he was told about a suspected drunk driver.
Police say he found the driver, who failed a breath test, before turning on the constable and knocking him unconscious.
The alleged attacker fled into heavy bush near the Tongariro River, but was found by a police dog.
A 22-year-old man will appear in court on Monday morning.
