Provided are device for assembling groups of eyebrow beautifying needles and method therefor. The assembling device comprises a base, a sliding block including two resilient members biased between the base and the sliding block, a central fastener for fastening the sliding block on or above the base, a holding assembly comprising a plurality of clamping posts vertically disposed on the base, and a plurality of holes with the sliding blocks passed through. Groups of eyebrow beautifying needles are adapted to insert into holding heads of the clamping posts with needle tips being flush in the holding heads of the clamping posts, and the needles in each group are fastened together by soldering. Moreover, sleeves of different colors or marks may be put on the needle groups for facilitating identifying the number of needles in each group.