The Aussie has won her 11th consecutive match in Miami behind five breaks of serve and 27 winners while defeating the Ukrainian for just the second time in seven career meetings.
Aussie continues imperious form to reach final
Barty set up break point in the opening game of the match and she converted after a slice drew an error from Svitolina's forehand.
The Ukrainian saved a break point to hold and stay within touch at 2-1. She wasn't as fortunate in her next service game as she was broken to love as Barty now led 4-1.
Svitolina got one of the breaks back and a subsequent hold pulled her to within 4-3, but the top seed closed strong, winning the final two games, converting on her second set point as the Ukrainian flew a backhand long.
Barty continued to apply pressure on Svitolina's serve and after the Ukrainian saved three break points in the opening game of the second set, she was broken in the fourth game after missing on another backhand.
The world number one was broken back, but restored her advantage straightaway for a 4-2 lead. Serving for the match, a forehand winner on match point wrapped up a most impressive performance.