Nick Reiner will head to court Wednesday morning for the preliminary hearing in his parents' double-murder case.

He'll appear before a judge at 8:30 AM at the Clara Shortridge Foltz Criminal Justice Center in Los Angeles ... where prosecutors will present evidence to determine whether or not he'll go to trial.

As you know ... Nick has been charged with murdering his parents, Michele and Rob Reiner, back in December. They were found brutally stabbed to death in their Brentwood home.

Nick has pleaded not guilty to the charges -- which include a special circumstances allegation that puts the death penalty on the table.

He was initially represented by attorney Alan Jackson, but the powerhouse lawyer dropped the case back in January. Instead, Nick is now being represented by public defender Kimberly Greene.

Nick has been held without bail at the Twin Towers Correctional Facility in L.A. ... the same jail D4vd's been transferred to after being charged with murdering 14-year-old Celeste Rivas.