PURPOSE: A partially and fully earth-anchored cable-stayed bridge using a main span prestressing unit and a construction method thereof are provided to efficiently generate tensile stress in deck segments installed in a middle span and to easily control the tensile stress. CONSTITUTION: A construction method of a partially and fully earth-anchored cable-stayed bridge using a main span prestressing unit is as follows. First and second main towers(111,112) separated in a bridge axis direction are installed. A first anchorage(113) is installed toward the outer side span of the first tower. A second anchorage(114) is installed toward the outer side span of the second tower. Stay cables(300) are extended from the first and second anchorages to a main span through the first and second main towers. Tensile stress is applied to first main span deck segments(130) by connecting the stay cables to the main span deck segments. First and second anchoring devices(410,420) are installed in the main span deck segments. A tension member(430) is installed between the first and second anchoring devices. When the main span deck segments are connected to each other in a bridge axis direction, the tension member is tensed. Side span segments(170) are installed from the first and second main towers.