A mechanism for folding and unfolding the top of a tent includes a connecting seat, a sliding seat and an elastic telescopic part. The connecting seat is connected with a tent top rod in a pivoted mode, and the sliding seat is connected with a connecting part in a pivoted mode and moves up and down with respect to the connecting seat. The other end of the connecting part is connected onto the tent top rod in a pivoted mode. The middle portion of the connecting seat extends downwards to form an accommodating seat which accommodates the elastic telescopic part. The upper portion of the sliding seat forms a sinking seat which has an inner diameter larger than an outer diameter of the accommodating seat.