Dina Lohan’s going to spend some time behind bars … after copping a plea in her DWI case.

A spokesperson with the Nassau County D.A.’s Office tells TMZ … Lindsay Lohan’s mom pled guilty to operating a motor vehicle while intoxicated and leaving the scene of an incident without reporting it.

We’re told Dina will have to spend 18 days in jail and will then be on 5 years probation. She also must participate in a victim impact panel and take part in an alcohol program.

As we reported … Dina was busted back in January after cops say an outing at Outback Steakhouse ended with her t-boning another car outside the restaurant and leaving the scene.

Cops ultimately tracked her down at her Long Island home … where cops say she fell on her face and accused the responding officer of pushing her. Cops said they detected a strong odor of booze on her breath and noticed Dina had glassy, bloodshot eyes too.

BTW … Dina had a prior DWI in 2013 also in Long Island.

We’ve reached out to Dina’s attorney for comment, so far no word back.