The 31-year-old policewoman was taken to hospital, a police spokesman said, while the 18-year-old soldier was taken in custody by British military police.
The assault happened in the town of Bad Fallingbostel, where there is a British army base.
The policewoman and a male colleague on patrol came across the brawl between the soldiers and locals. After calling for backup, they tried to break up the men.
But the men fled into a park. As the officers gave chase, the accused soldier allegedly turned on her and punched her repeatedly in the face and around the head.
He also tried to attack the second officer, who came to her rescue, but was stopped by the local men with whom he’d been brawling. The woman was left dazed and bleeding heavily.
Only when the police reinforcements arrived could the drunken soldier be subdued and arrested.
German police took an alcohol reading of the man before handing him over to British military police.