Porn legend Jenna Jameson insists ... she was not under the influence when she slammed her car into a pole back in May -- pleading "not guilty" today to DUI.
TMZ broke the story ... Jameson was arrested after the single-car accident in Orange County May 25th. Cops said she showed signs of intoxication, failed a field sobriety test, and was subsequently busted on suspicion of DUI.
According to law enforcement, Jenna blew a .13 and had two prescription drugs in her system at the time of her arrest -- zolpidem (Ambien) and buprenorphine (Suboxone).
A pretrial hearing has been set for August 16. If convicted, Jenna faces up to a year in jail.