Former UFC star Diego Sanchez is back behind bars ... after cops in New Mexico busted him for allegedly driving drunk.

Sanchez was arrested Monday by the Socorro City Police Department and booked into the Socorro County Jail, records show. He's facing an aggravated DUI charge, along with a probation violation.

According to the booking info, Diego's blood-alcohol level was allegedly greater than .16 ... more than twice the legal limit.

And that could be an especially big problem for Sanchez.

Earlier this year, a judge sentenced him to five years of supervised probation after he fired a gun into the air from a Jeep in Albuquerque ... and one condition of that probation required Sanchez to stay away from alcohol.

As TMZ previously reported ... Sanchez narrowly avoided prison in that case, getting five years of supervised probation and 800 hours of community service despite prosecutors pushing for time behind bars.

TMZ also reported in May that Sanchez and his wife, Teresa Tapia, had divorced amid his legal troubles.

The 44-year-old was booked around 5:17 PM and, according to jail records, had no bond set.

Now, the alleged DUI could put the freedom he kept earlier this year in jeopardy.