Disclosed is a method for preparing broccoli with increased sulforaphane content using high-voltage pulsed electric field treatment. According to the method, broccoli with increased sulforaphane content can be eaten raw or can be chopped to appropriate sizes before eating without the need to crush the broccoli. In addition, sulforaphane can be extracted from the broccoli with increased sulforaphane content. The broccoli with increased sulforaphane content and the sulforaphane extract produced therefrom can be used as an active ingredient of a food, feed or cosmetic composition to exhibit the activities of sulforaphane, including antioxidative and anti-inflammatory activities.