The invention discloses an electrodeless mercury lamp which comprises a lens set, a mercury bulb, an excitation source and a temperature control device. The mercury bulb comprises a light-emitting part and a cold end part communicated with the light-emitting part, the light-emitting part is cylindrical, the cold end part is cylindrical or in a cuboid shape, and the diameter of the connecting portion of the light-emitting part and the cold end part is smaller than that of the light-emitting part. The mercury bulb is filled with pure mercury or isotope Hg2O2. A double-bulb structure is adopted for the mercury bulb, bulb bodies for emitting light and storing mercury are subjected to function separation, meanwhile, the light-emitting part and the cold end part are communicated through the small-diameter connecting portion, the light-emitting part is coupled with an external coil to emit light, and the cold end part stores mercury and is connected with the temperature control device. By means of the structure, liquid-state mercury cannot flow in into the light-emitting part easily, and the phenomenon that mercury permeates into bulb walls of the light-emitting part to be nebulized due to loss is weakened. In addition, common cold ends are mostly thin and short, the cold end part and the light-emitting part are almost identical in size, the contact area of the cold end and the temperature control device is large, and heat radiation temperature control is easy.