A speech assessment device and method for a multisyllabic-word learning machine, and a method for visualizing continuous audio are provided. By performing the step of starting the assessment mode, the step of selecting words to be assessed, the step of choosing to play or record, the step of recording, the step of visualization (including the step of picking out fundamental frequency, the step of defining analysis point, the step of transforming polygonal lines, and the step of simplifying the polygonal lines), the step of repeating, and the step of assessment, the speech assessment device and method for a multisyllabic-word learning machine are capable of providing assistance in oral language learning, and capable of rehabilitating patients with hearing impairment through visual aids.