A method and device of automatic detection and modification of subtitle position comprises the steps of comparing an active display area parameter of a displaying device to an original subtitle control signal to generate a comparison result, and outputting a targeted subtitle control signal to modify the position of the subtitle depends on the comparison result so that the subtitle is guaranteed to display in the active display area. Accordingly, the subtitle position detection and modification method and device may not only as a solution of improper subtitle display position arrangement, but also excite the viewer's joy of the sight and eliminate the inconvenience of the complicated adjusting operations.