The invention relates to a lamp holder assembly fixture and a lamp holder assembly method. The lamp holder assembly fixture comprises a mounting seat, a floating needle and an elastic mechanism, wherein the upper end of the mounting seat is provided with a positioning end, a lamp head fixing part is arranged above the positioning end, a nut mounting groove is formed in the upper end surface of the lamp head fixing part, a floating needle through hole is downwards formed in the middle part of the nut mounting groove, the floating needle is arranged in the floating needle through hole in a penetrating way, and the upper end of the floating needle is provided with a guide end. The lamp holder assembly fixture has the advantages that when a lamp holder is mounted, the lamp head can be fixedly arranged on the lamp head fixing part, a lamp holder housing sleeves the positioning end of the mounting seat, and the guide end of the floating needle sequentially passes through the mounting through hole of the lamp head and the mounting through hole of the lamp holder housing, and is exposed out of one side, away from the lamp head, of the lamp holder housing, so the guide function on a bolt is realized, the mounting positions of the nut, the lamp head, the lamp holder housing and the bolt are automatically aligned, and the artificial error is effectively avoided; the assembly structure is reliable and convenient, the assembly time is saved, the error rate of assembly is reduced, and the production efficiency is improved.