The invention relates to a fuel assembly and a tube base for the fuel assembly. The tube base comprises a pore plate and a support mechanism, wherein through holes are distributed on the pore plate; the support mechanism is arranged on one side of the pore plate; the support mechanism comprises at least one arc-shaped rib plate arranged on the pore plate; an arc-shaped opening is formed in one side, distant from the pore plate, of the arc-shaped rib plate; the opening of the arc-shaped opening faces one side, distant from the pore plate. An arch bridge type arc-shaped rib plate can effectively avoid the stress concentration between a lower pore plate and a support leg and the continuous distribution of the stress of a lower tube base is more uniform, so that the strength of the lower tube base can be increased; besides, a refrigerant flows upward from the lower end; the incident flow area of the arch bridge type arc-shaped rib plate in equal thickness is gradually upward changed along the axial direction, the violent change of the flow resistance when the refrigerant flows is reduced and the flow field is improved; for an integrated lower tube base, the removed blank is reduced and the use ratio of the material is increased.