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Currently, the paper softness testing instruments have the problem that the range is small and the applicable object is little. A method for grading the softness of the paper was proposed, which is based on the differences of sound energy feature, hit-point energy and principal component analysis (PCA). Firstly, Hit point energy law given the test object softness reference value, and framed audio signals for different softness of the paper and obtained the energy of each frame. Then the PCA was used to obtain characteristics unrelated training set and established the characteristic matrix. Finally, the softness levels of the paper was determined by the principle of minimum variance. Experiments showed that the paper softness could be divided into five different levels, and the correct rated of 100%.