Abstract: The Principle of innocence presumption for science technology is a methodological principle for appraising the social values of science and technology. Three rules for appraising the harm of science technology are derived from the principle. That is the proof duty being under taken by the skeptic, the doubted science and technology dispensing with pleading,and beneficial to the doubted science and technology. On the basis of the principle "science technology is the first productivity", it is significant to stick to the principle for the development of science and technology. The principle establishes a scientific logic of appraising the social values of science and technology for the principle insures the establishment of a good system of appraising science and technology and preventing science and technology to be censured for no reason. The principle establishes the indispensable development right of science and technology and enhances the duty consciousness, the level of the knowledge of science technology and the level of appraising science and technology of the skeptic.