Dennis Quaid's twins are graduating from high school soon ... and he's going to court to make sure that means he's graduating from his child support obligations!

Here's the situation -- the "War Machine" star is currently paying $13,750 per month in child support -- plus additional amounts if his income exceeds a certain amount -- to his ex, Kimberly Buffington. Their 18-year-old daughter, Zoe, graduated from high school on May 23, and her twin brother, Thomas, is graduating on June 3 ... and Dennis wants to clarify that his child support payments should be terminated upon their respective graduations!

He is also asking the court that any additional payments based on his income are prorated to the date of his kiddos' high school graduation dates rather than his full-year income.

Dennis previously submitted court docs about child support back in 2020 ... telling the judge he's happy to cough up more cash with his fluctuating income, as long as it's reasonable.

Dennis and Kimberly filed for divorce in 2016 -- the couple's second time separating -- and finalized their divorce in 2018 after 14 years of marriage.

Dennis was also married to actress Meg Ryan, and they share a son, Jack Quaid. Dennis was first married to actress P.J. Soles.

He married his fourth wife, Laura Savoie, in June 2020.