A heat sink, including a heat sink body and a filling material. A through hole is disposed in a position, corresponding to a to-be-cooled electronic element, on the heat sink body. The to-be-cooled electronic element is mounted on a circuit board and located between the circuit board and the heat sink body. There is a gap between the to-be-cooled electronic element and the heat sink body. The gap is connected to the through hole. The filling material is injected into the through hole and fills the gap. The present invention further discloses a heat dissipation system having the heat sink. The heat sink resolves problems in the prior art that, a heat sink has low thermal conduction efficiency and it is difficult to control a filling volume of a thermally conductive material in a gap between a heat sink and a chip.