The present invention relates to a mouthpiece device of an electronic cigarette, includes an atomizing device for vaporizing tobacco substance into aerosol, a reservoir for storing tobacco substance and a guiding tube for guiding tobacco substance from the reservoir to the atomizing device, which are all set in a shell. The guiding tube has one end inserted in the reservoir and the other end communicated with atomizing device. The mouthpiece device further includes a preheating device for heating solid tobacco substance in the reservoir to generate liquid. The preheating device is set in the end of the reservoir near the guiding tube, and seals solid tobacco substance in the reservoir. The present invention solves existing problems such as fluid leakage, complicate manufacturing, high cost, bad heat insulation and filtering aerosol; and obtains perfect leakage proof, simple manufacturing, lower cost, good heat insulation and well filtering aerosol.