An ultrasound imaging apparatus comprising: a display unit configured to display an ultrasound image and an external image such that a first reference line overlaps the ultrasound image and a second reference line overlaps the external image; an ultrasound probe configured to irradiate an ultrasound signal to an object and receive an echo ultrasound signal from an object; and a controller configured to receive a command for moving or rotating at least one image of the ultrasound image and the external image based on a predetermined reference coordinate system through the ultrasound probe, to determine whether the ultrasound image matches with the external image according to manipulation of the ultrasound probe, and to control the display unit to synthesize the ultrasound image with the external image and to display the ultrasound image and the external image, if determining that the ultrasound image matches with the external image, characterized in that if a command for selecting a first reference point of the ultrasound image is input by the user, the controller fixes the ultrasound image including the first reference point, determines whether the fixed ultrasound image matches with the external image changing in correspondence to movement of the ultrasound probe adjusted by a user, based on the first reference line displayed on the ultrasound image and the second reference line displayed on the external image, and controls the display unit to synchronize the ultrasound image with the external image and to display the ultrasound image and the external image, if determining that the ultrasound image matches with the external image, or if a command for selecting a second reference point of the external image is input by the user, the controller fixes the external image including the second reference point, determines whether the fixed external image matches with the ultrasound image changing in correspondence to movement of the ultrasound probe adjusted by the user, based on the first reference line displayed on the ultrasound image and the second reference line displayed on the external image, and controls the display unit to synchronize the ultrasound image with the external image and to display the ultrasound image and the external image, if determining that the external image matches with the ultrasound image. a display unit configured to display an ultrasound image and an external image such that a first reference line overlaps the ultrasound image and a second reference line overlaps the external image; an ultrasound probe configured to irradiate an ultrasound signal to an object and receive an echo ultrasound signal from an object; and a controller configured to receive a command for moving or rotating at least one image of the ultrasound image and the external image based on a predetermined reference coordinate system through the ultrasound probe, to determine whether the ultrasound image matches with the external image according to manipulation of the ultrasound probe, and to control the display unit to synthesize the ultrasound image with the external image and to display the ultrasound image and the external image, if determining that the ultrasound image matches with the external image, characterized in that if a command for selecting a first reference point of the ultrasound image is input by the user, the controller fixes the ultrasound image including the first reference point, determines whether the fixed ultrasound image matches with the external image changing in correspondence to movement of the ultrasound probe adjusted by a user, based on the first reference line displayed on the ultrasound image and the second reference line displayed on the external image, and controls the display unit to synchronize the ultrasound image with the external image and to display the ultrasound image and the external image, if determining that the ultrasound image matches with the external image, or if a command for selecting a second reference point of the external image is input by the user, the controller fixes the external image including the second reference point, determines whether the fixed external image matches with the ultrasound image changing in correspondence to movement of the ultrasound probe adjusted by the user, based on the first reference line displayed on the ultrasound image and the second reference line displayed on the external image, and controls the display unit to synchronize the ultrasound image with the external image and to display the ultrasound image and the external image, if determining that the external image matches with the ultrasound image.