A method of detecting the alignment error of lenses and reducing image distortion attributable to the alignment error in a lens-type 3-dimensional liquid crystal display monitor. A method of detecting the alignment error of lenses in a 3D display using a purpose-built test pattern image, which predicts the alignment error in such a way as to calculate variation in view indices of pixels in a lateral direction, observed by an eye of an observer, if there is alignment error in the lenses. A method of compensating for image distortion in a 3D monitor, including the steps of finding the relationship between the pixels of a Liquid Crystal Display (LDC) panel and the pixels of observed images, which are determined depending on the location of an observer; and compensating for image distortion attributable to the rotational and translational alignment error of the lenses based on the found relationship.