An inner coupling tubular type electrodeless lamp comprises a glass bulb, an amalgam, and a power coupler. The glass bulb includes an external portion and an inner portion. A gas discharging cavity that is annularly airtight is defined by an envelopment of the external portion and the inner portion. A coupling cavity is defined in the inner portion. The power coupler includes a radiating post, a ferrite core, and a winding sequentially situating from an interior to an exterior thereof. The power coupler is disposed in the coupling cavity. Two ends of the coupling cavity are intercommunicated with each other as well as the exterior. The external portion of the glass bulb adopts the elongated tube. Wherein, a length of the ferrite core of the power coupler is not smaller than a half length of the coupling cavity. A length of the winding is measured from one-fifth to four-fifth of the length of the coupling cavity to evenly distribute an electromagnetic field. At least one diffuse reflection layer that is made of a material falling in a 250˜2000 nm spectrum scope is disposed between an inner wall of the inner portion (the side near the power coupler) and an external surface of the power coupler. Wherein, the material for making the diffuse reflection layer adopts a non-conducting electricity material that resists a temperature higher than 100° C.