Abstract: A portable computer system for expanding usage function includes an independent host unit and a function expansion unit. The host unit at least includes a motherboard module, a first power supply module, a display module, a wireless transmission module, and a first I/O interface module. The motherboard module, the first power supply module, the display module, the wireless transmission module and the first I/O interface module are electrically connected with the motherboard module. In addition, the display module has a built-in touch pad. The function expansion unit at least includes a keyboard module and a bracket module. The keyboard module is electrically connected with the motherboard module of the host unit. The bracket module is pivoted on the keyboard module, and the bracket module is detachably and electrically connected with the host unit.