The present disclosure provides a device for detecting a rotation angle of a prism and a method for using the same. The device for detecting a rotation angle of a prism is configured to detect, in the case that a prism film plate of a backlight module rotates relative to a display panel until the display panel displays a predetermined image, a rotation angle of the prism film plate relative to the display panel. The device for detecting a rotation angle of a prism includes: a stationary protractor; a film plate clamping mechanism configured to clamp the prism film plate; and a rotation mechanism which rotates the film plate clamping mechanism around an axis of the protractor. When the rotation mechanism drives the film plate clamping mechanism to rotate and the film plate clamping mechanism drives the prism film plate to rotate until the display panel displays the predetermined image, the rotation angle is detected based on an angle by which the film plate clamping mechanism rotates relative to the protractor.