Ultrasonically assisted extraction (UAE) technique was developed for the simultaneous extraction of three main flavonoids, that is, isoorientin, orientin, and vitexin, from bamboo leaves of N. affinis, a discarded waste in the locality in this present work. Extraction conditions for each compound were optimized by factorial design coupled with exploration of interaction among factors using selectivity and yield of total flavonoids as evaluation indexes. The optimum conditions for UAE of these flavonoids were obtained. Recovery test and repeatability analysis of UAE technique under the optimized conditions was proven to be satisfactory for flavonoids investigated. Compared with the conventional refluxing extraction, ultrasonic method produces higher yields for each of flavonoids investigated and total flavonoids, with comparable selectivity for three flavonoids. Highly effective extraction of ultrasonic technique for flavonoids indicated it application prospect in the extraction of topic plant.