The west London club, in a statement on their website (www.qpr.co.uk), also warned Barton that he could be shown the door if he did not stay out of trouble.
'The club has... reached agreement with Barton that if he seriously breaches the club's disciplinary procedures again, the club reserves the right to terminate his contract,' the statement said.
Barton was handed a 12-match ban in May after being found guilty of violent conduct in QPR's final match of last season against Manchester City. Barton, who was also fined 75,000 pounds (S$149,736) last month, was sent off in the 54th minute for elbowing Carlos Tevez and then kicking Sergio Aguero in the match that crowned City as champions.
He also appeared to try and head-butt City defender Vincent Kompany before being escorted off the pitch.
"It was important that we took our time to make sure we came to the correct decision, which I believe we have achieved," QPR chief executive Philip Beard said.
"Joey’s behaviour, which led to his red card at Manchester City, and his subsequent actions were completely unacceptable and we have made our feelings on this matter known to him."
Barton, 29, will also miss QPR’s pre-season tour of Asia next month.
"My behaviour was wrong and I accept the punishment that has been imposed upon me as a result," the website quoted the former Manchester City player, who has a long history of trouble on and off the field, as saying.
"I apologise to the manager, my team-mates and of course the QPR fans for my actions. I also apologise to the Manchester City players, staff and supporters."