The present invention relates to an electronic cigarette for convenient injection of cigarette liquid, manufacturing method thereof, and a method for injecting cigarette liquid into the electronic cigarette. A liquid injection hole is opened at a bottom of a liquid storage cup of the electronic cigarette, and the liquid injection hole is sealed by a sealing element which is self-closing once an injection device has been pulled out from the sealing element. The components of the electronic cigarette of the present invention can be assembled together first prior to the injection of cigarette liquid. Therefore, the problem of leakage and contamination of cigarette liquid during the manufacture of existing electronic cigarettes can be overcome. The automated injection of cigarette liquid can be carried out at places where the electronic cigarettes are sold.