An electrical connector comprising a terminal module and a housing. The terminal module comprises a plurality of terminals. The housing comprises an accommodating groove in which the terminal module is disposed. The accommodating groove comprises a first groove wall and a second groove wall opposite to the first groove wall. The terminal module is disposed between the first groove wall and the second groove wall. A wall surface of the first groove wall and a wall surface of the second groove wall are disposed close to a structural contour of the plurality of terminals. Since the groove wall is designed as a wall surface close to the structural contours of the plurality of terminals, the dielectric constant of the groove wall can be greater than that of the air. In this way, the relative dielectric constant around the plurality of terminals would be increased to reduce the impedance.