An arched window covering includes a shade mount and a shade mounted on the shade mount. The shade mount has a base, at least a spacer, and two rails. The spacer is provided on the base and its width is adjustable. The rails movably engage the base and touch the spacer that a length of the shade mount is changeable by changing the width of the spacer. Therefore, a size of a shade mounted on the shade mount is changeable by adjusting the spacer rather than cutting the rail to fit the windows with different sizes.