The invention discloses an electronic cigarette allowing liquid to be injected from the top and a heating assembly to be replaced at the bottom. The electronic cigarette comprises a cigarette holder, a connection assembly, a liquid storage tube and the heating assembly, wherein the cigarette holder, the connection assembly, the liquid storage tube and the heating assembly are sequentially connected from top to bottom. The connection assembly is connected with the cigarette holder and the liquid storage tube, the heating assembly is detachably connected with the lower end of the liquid storage tube, a partition board is disposed in the liquid storage tube and divides an inner cavity of the liquid storage tube into an upper containing cavity and a lower containing cavity, the partition board is provided with a liquid discharge hole, a rotatable atomizing tube is arranged on the upper portion of the partition board, the lower end of the atomizing tube extends to form a block used for plugging the liquid discharge hole in the radial direction, the upper end of the atomizing tube penetrates through the connection assembly and then is inserted into the cigarette holder, an upper end port of the atomizing tube is communicated with the cigarette holder, and a lower end port of the atomizing tube is communicated with a smoke outlet of the heating assembly. According to the electronic cigarette, the electronic cigarette can be filled with the tobacco liquid conveniently and hygienically, heating and atomizing amount of the tobacco liquid can be adjusted through the heating assembly, taste is improved, and the heating assembly can be conveniently replaced according to needs.