The invention provides a card substrate for carrying a chip module, the card substrate has a first surface and a second surface opposite to the first surface, and a concave portion for accommodating the chip module, the concave portion includes a first concave portion, and a second concave portion further recessed from a bottom wall of the first concave portion, in a left-right direction, a size of the second concave portion gradually narrows from a middle to both sides, and in an up-down direction, the size of the second concave portion gradually narrows from the middle to both sides. The card substrate of the invention can provide good support and protect for the chip module.