An electrical connector assembly includes a board end connector and a wire end connector. The board end connector includes a board end connector shell and a board end connector body. The wire end connector includes a wire end case and a tongue plate. At least one guide piece is extended from one of the board end connector shell and the wire end case, and a remaining one of the board end connector shell and the wire end case is provided with at least one guide slot for creating a butt joint with the guide piece. The electrical connector assembly of the present disclosure utilizes the space of the board end to the maximum extent, solves the problem that the CPU occupies the space of the board end due to the increased size of the heat dissipation module, and can realize high-speed data transmission.