Abstract: The present disclosure relates to a hydrophobically modified nanocellulose crystal and a method for hydrophobic grafting modification of nanocellulose crystals, comprising the steps: mixing the nanocellulose crystals with a saturated alkane, and stirring the resultant at room temperature or under a heating condition; while stirring, adding in sequence a polymethylhydrosiloxane containing a silicon-hydrogen bond and a catalyst; continuously stirring to complete the dehydrogenation reaction, then obtaining a mixed solution; and filtering the mixed solution by a polyvinylidene fluoride membrane, then drying it to complete the hydrophobic modification. A —Si—O—C-chemical bonding is formed between the polymethylhydrosiloxane and the nanocellulose crystal in the method, enabling improvement of the hydrophobicity and water resistance of the nanocellulose crystal.