A heat sink includes a base and a plurality of fins. A root of the fin is connected to the base. A heated area, a dropping pipe, and a spacing strip between the heated area and the dropping pipe are formed in the fin. A first passage and a second passage are formed between the heated area and the dropping pipe. A hydraulic diameter of a pipeline in the heated area is less than a critical dimension. A hydraulic diameter of a pipeline of the dropping pipe is greater than or equal to the critical dimension, and a pressure of liquid at an intersection of the second passage and the dropping pipe is greater than a pressure of liquid at an intersection of the second passage and the heated area.