Sam Worthington -- Sued For $10 Million ... Accused Of Beating Paparazzi

Sam Worthington and his girlfriend are now facing a $10 million lawsuit ... stemming from their violent run-in with a paparazzo in NYC earlier this year.

According to the docs ... Sheng Li accuses Sam and GF Lara Bingle of viciously assaulting him in February outside a bar where he was snapping photos.

Both are also being accused of slander and libel ... for allegedly making false statements about him to the NYPD.

Li says he suffered a torn shoulder, facial contusions, injuries to his thumb and wrist, and adds he might need surgery ... according to the docs.