A cover assembly for a trash bin includes a cover, a support ring, a pivoting device coupling to the cover and the support ring and a buffer device connecting to the pivoting device. The pivoting device provides an upward force to the cover, and the buffer device cushions the upward force from the pivoting device. The buffer device and the pivoting device allow the cover assembly to be lifted slowly and prevent a loud noise while lifting the cover quickly and while the cover bumps the trash bin.