The invention discloses a 2 dimensional digital image related compensation method based on transformation of coordinates and a 2 dimensional optical digital image related extensometer, and relates to the field of non-contact type optical measuring. According to the invention, in order to address the in-plane deformation of a panel test specimen in 2 dimensional digital image related measuring, due to the error caused by out-of-plane displacement, the method and related compensation method and the related extensometer can be applied to accurate measuring of the in-plane deformation of the panel test specimen. According to the invention, the method is based on the transformation of coordinates of a compensation plate, and the acquisition of a single frame image can real-time acquire the out-of-plate displacement and rotation information of the compensation plate, thus removing the effects on the result of measuring by the out-of-plate displacement and rotation information. The method overcomes the problems of excessively large errors or smaller requirement angle of traditional measuring methods, and can be applied to real-time measuring of in-plane deformation of a 2 dimensional panel test specimen.