A countertop installation assembly comprises an installation seat, a driving member, and a fastening assembly. The installation seat is positioned in the installation hole and is configured to extend to below the countertop. The installation seat comprises a receiving cavity extending along a longitudinal direction. The driving member is rotatably disposed in the installation seat. The fastening assembly is operatively coupled to the driving member, and the fastening assembly is located below the countertop and moves up and down in the receiving cavity. The driving member is rotated from above the countertop to drive the fastening assembly to move up and down in the receiving cavity so as to enable the fastening assembly to be clamped to or separated from a lower side of the countertop. The fastening assembly is driven by the driving member to move between a retracted position and an extended position.