An atomizer for an electronic cigarette, comprising: a housing having a first end and an opposite second end, the second end being configured for connecting with a power supply, the housing defining a liquid chamber configured for containing tobacco liquid; a sealing cover threadedly coupled with the first end; an atomizing element arranged in the housing, the atomizing element being configured for atomizing the tobacco liquid to form aerosol; an air passage defined in the housing; an liquid injecting opening defined in the first end, the liquid injecting opening being in communication with the liquid chamber; wherein the sealing cover comprises a device configured for preventing children from screwing off the sealing cover, the sealing cover can be screwed off via an outer surface thereof only when an external force is exerted on the device to change an internal structural relationship of the device, characterized in that the sealing cover is configured for sealing the liquid injecting opening, wherein the sealing cover comprises a main body threadedly coupled to the first end, and a protective cover nesting the main body; the device comprises a spring, a first protrusion, and a groove, the spring is arranged between the main body and the protective cover, the first protrusion is arranged on one of the main body and the protective cover, and the groove is defined in the other of the main body and the protective cover, the groove matches with the first protrusion; the spring makes the groove disengaged with the first protrusion; when an external force is exerted the main body along an axial direction of the main body to overcome an elastic force of the spring, the first protrusion is engaged with the groove, so that the protective cover is capable of driving the main body to rotate, thus separating the sealing cover from the first end. a housing having a first end and an opposite second end, the second end being configured for connecting with a power supply, the housing defining a liquid chamber configured for containing tobacco liquid; a sealing cover threadedly coupled with the first end; an atomizing element arranged in the housing, the atomizing element being configured for atomizing the tobacco liquid to form aerosol; an air passage defined in the housing; an liquid injecting opening defined in the first end, the liquid injecting opening being in communication with the liquid chamber; wherein the sealing cover comprises a device configured for preventing children from screwing off the sealing cover, the sealing cover can be screwed off via an outer surface thereof only when an external force is exerted on the device to change an internal structural relationship of the device, characterized in that the sealing cover is configured for sealing the liquid injecting opening, wherein the sealing cover comprises a main body threadedly coupled to the first end, and a protective cover nesting the main body; the device comprises a spring, a first protrusion, and a groove, the spring is arranged between the main body and the protective cover, the first protrusion is arranged on one of the main body and the protective cover, and the groove is defined in the other of the main body and the protective cover, the groove matches with the first protrusion; the spring makes the groove disengaged with the first protrusion; when an external force is exerted the main body along an axial direction of the main body to overcome an elastic force of the spring, the first protrusion is engaged with the groove, so that the protective cover is capable of driving the main body to rotate, thus separating the sealing cover from the first end.