Ali Brown smashed 176 from just 97 balls and put on 296 for the first wicket with James Benning (152) while Rikki Clarke hit an unbeaten 82 from only 28 balls as Surrey recorded the highest total in a List A limited-overs match.
The previous best was the 443-9 achieved by Sri Lanka against the Netherlands last year while Surrey's previous best was 438 against Glamorgan five years ago when Brown scored 268.
Surrey bowled out Gloucestershire for 239 to win the match by 257 runs.
Elsewhere England opener Marcus Trescothick continued his rehabilitation from the stress-related illness that cut short his Ashes tour and kept him out of the World Cup with 58 off 43 balls for Somerset against Sussex.
Trescothick's innings was not enough to save his team from defeat with Sussex winning by 38 runs.
Surrey 496 for 4 in 50 overs (Ali Brown 176, James Benning 152, Rikki Clarke 82 n o) bt Gloucestershire 239 all out in 48 overs.
Somerset lost to Sussex by 38 runs.