A tower computer system includes a tower chassis; a mounting assembly installed at a middle section of a widthwise surface of the tower chassis and coupled to internal sides of the front and rear racks to form a vertical connecting board for providing a longitudinally perpendicular fixing position to a predetermined board, and acting as a longitudinal corresponding line formed by connecting the front rack to the rear rack for the connecting board of the mounting assembly, such that the transverse widthwise surface of the tower chassis is separated into a first assembling chamber with an opening aligned towards the left side and a second assembling chamber with an opening aligned towards the right side; and a first electric connection port, disposed in a vertical direction on the rear rack and at a position proximate to the mounting assembly, and situated in an area inside the first assembling chamber.