The utility model relates to the technical field of a lighting fitting, especially a built-in lamp assembling structure of a desk lamp. The utility model comprises a semiclosed connection frame body, a first conducting wire tube and a second conducting wire tube, wherein the semiclosed connection frame body is provided with two sets of opposite end surfaces, one set of the end surfaces are provided with through holes and the first conducting wire tube and the second conducting wire tube are respectively connected and fixed on the outer side of the end surfaces by nuts. The structure of the utility model is simple, a traditional desk lamp which is only provided with an outer lamp structure is changed, and the built-in lamp assembling structure is added; not only an outer lamp or a built-in lamp can be selected for use according to a user's requirement, but also the utility model is favorable for power saving and can make the lighting fitting have more beautiful appearance during use.