The invention relates to an ultrasound therapy system, and more particularly to a focused ultrasound therapy device, which uses an image alignment and fusion method to guide the therapy. The therapy system provided by the invention comprises central control means, ultrasound energy application means, moving and locating means for ultrasound energy application means, real-time B-type ultrasound image guiding means. Moreover, the inventive system also has patient's posture fixing means, with the aid of which a real-time B-type ultrasound image is aligned with a diagnostic image, and on the basis of the alignment the B-­type ultrasound image and the diagnostic image are fused so as to guide the therapy. Compared to the known scheme in the art, the invention is effective and has low cost to resolve the high-intensity ultrasound focused therapy, and more particularly for the difficult tumor therapy problem it provides a very practical scheme, which can be easily used in clinical tumor therapies.