There were 148 arrests on Saturday and 162 arrests on Sunday, police said.
At least 50 people were arrested for allegedly attempting to use fake IDs at the mini-bars set up around the Fairplex grounds, police said. Others were arrested for offenses related to public intoxication, being under the influence of a controlled substance, possessing a controlled substance for personal use or for sales and driving under the influence.
The music festival included performances by Boys Noize, Skrillex, Glass Animals and Destructo.
Live Nation and Pomona police worked together to crack down on illegal behavior at the music festival following the deaths of two young women in August.
Katie Dix, 19, and Tracy Nguyen, 18, died of suspected drug overdoses after attending HARD Summer at the Fairplex.
The board recommended a temporary ban in the wake of their deaths and Live Nation and the nonprofit Los Angeles County Fair Association agreed to cancel a Sept. 10 rave at the Fairplex.
Live Nation implemented several significant health and safety conditions for HARD Day of the Dead, including decreasing attendance from 65,000 to 40,000 attendees per day, setting the age limit at 21 and over and increasing on-site medical and security services.
City News Service contributed to this report.