An atomizer includes an upper cover assembly, an atomizing device and a regulating assembly. The atomizing device is arranged between the upper cover assembly and the regulating assembly. The regulating assembly includes a regulating base and a regulating ring rotatably sleeved about the regulating base. The regulating base is provided with at least one first circulating portion in fluid communication with the atomizing device. The regulating ring is provided with a second circulating portion arranged corresponding to the first circulating portion. An area of communication between the first circulating portion and the second circulating portion is changed by rotating the regulating ring. The atomizer has a good leak-proof function.