The present invention discloses tuna bone powder and a preparation method thereof. High-quality tuna bones are repeatedly washed clean and drained for a standby application, then a subcritical water combined microwave treatment is used to enable fish bones to be fully softened, then after the fish bones are evenly mixed with a deodorant, putting still is conducted for 10-30 min, then the deodorantis washed clean with clean water, and finally the fish bones are dried, pulverized and sterilized to obtain the tuna bone powder. The subcritical water combined microwave treatment technology is usedfor processing the tuna bones, can effectively shorten softening time, enhances a softening effect, and reduces time cost loss. At the same time, the preparation method retains calcium, phosphorus and other nutritional components in the fish bones to the maximum extent, and avoids caused loss and waste of nutrients during the softening process. In addition, after the subcritical water combined microwave treatment, the preparation method lays foundation for late-stage deodorization, drying and pulverization, can effectively release minerals of hydroxyapatite, etc. in the fish bones, significantly increases protein content in the fish bones, and enables nutrients in the fine powder to be more liable to be digested and absorbed by human body.