As one of the common image distortions in fiber plate, the imaging quality and accuracy of relative components are influenced by magnification image distortion greatly. Distribution of magnification image distortion in fiber plate is researched. Changing trend of horizontal magnification in plate is from high to low then grows high gradually and there is an abrupt area close to edges. Center magnification is the lowest at vertical and magnifications at both ends are the highest. According to forced states of single fiber at local micro area, producing reasons and influence factors of the magnification distribution are analyzed. Magnification image distortion is controlled in 1% effectively by adding lubricating materials and optimizing process parameters such as thermo-forming temperature and suppressed scale etc. of roughcast sections of optical fiber plates.