Blac Chyna's trying to pull the plug on a deal she made with her ex, Rob Kardashian, to end their legal war over revenge porn ... at least according to Rob, who now wants a judge to make her stick to the deal.

In new docs filed Monday by Rob's attorneys, he says his ex agreed to drop her lawsuit against him for revenge porn, IF he helped get her dropped from a separate lawsuit. As we reported, one of BC's exes, Pilot Jones, filed suit against Chyna and Rob, claiming they'd outed him as gay, and thereby exposed him to public threats.

According to Rob, the deal between Chyna and himself was that he would get her out of that Jones lawsuit without it costing her a cent ... and she would drop the revenge porn case. Rob says he accepted that deal last month, but now Chyna's trying to get cute.

In the docs, obtained by TMZ, he says Chyna is threatening to push forward with a trial in the revenge porn case ... exactly what he had hoped to avoid when he struck the deal with her.

Rob says she needs to drop the case altogether, because he accepted the terms of the deal. As a result, he's asking a judge to enforce that contract.

Gotta imagine, Rob's really doesn't want another drawn-out public trial with the mother of his daughter ... having just gone through one over their reality show getting canceled.

Remember, the Kardashians soundly defeated Chyna in that one, but in the docs, Rob says she's itching for a second fight ... in court. The revenge porn trial is scheduled to begin next week.

The judge has yet to rule on Rob's request, but he wants an emergency hearing to address the matter.