The invention relates to a preparation of tissue slice, and discloses a dehydration method of tissue block, comprising the following steps: dehydrating the fixed tissue block in gradient by ethanol aqueous solution with volume percent 70% to 100% at room temperature, using ultrasonic wave 2 to 5 times during processing of gradient dehydration by ethanol aqueous solution, 4 to 40 min each time. The invention further discloses application of the tissue block ultrasonic wave dehydration method in preparation of tissue slice. The invention reduces dehydration time of tissue block without reducingslice quality of tissue slice. The invention is especially appropriate for preparation of tissue slice with high quality.