A window covering comprises an upper rail, a window shade located below the upper rail, a lower rail located below the window shade, a first clamping assembly and a second clamping assembly located at two sides of the lower rail and spaced from each other, and a cord winding assembly located in the lower rail to connect to the first clamping assembly and the second clamping assembly. A first cord and a second cord run through two opposite sides of the window shade to fasten to the cord winding assembly. The lower rail can be moved upwards or downwards by a user to retract or expand the window shade through the first and second cord. Besides, the distal ends of the first and second cords can be hidden in the cord winding assembly in the lower rail, thus can prevent the cords from entangling children to avoid accidents.