An assembly for fixing and connecting a polygonal LED light bar lamp includes a fixing seat, a covering plug, and an electrical connector. The fixing seat has a bottom with both edges thereof extending to form two bevels and parallel plates. The bottom and bevels have a penetrating hole, respectively. The covering plug has a cover having an insertion hole. Two electrode pins are disposed in the interior of the insertion hole. The electrical connector has a partitioning block. Both sides of the partitioning block have a protruding pillar, respectively. The protruding pillar is provided with a hollow pillar having electrodes for contacting with electrode pins. With the fixing seat being fixed on a carrier, the light bar can be held in the fixing seat with adjustable irradiating direction. Further, two light bars can be connected in series by the electrical connector.