A vapor chamber system, includes a heat source and a vapor chamber device. The vapor chamber device includes a first casing, a second casing, a second capillary structure and a third capillary structure. The first casing includes a first plate, and a first capillary structure. The second casing is stacked on the first casing. The second capillary structure is disposed between the first capillary structure and the supporting posts of the second casing. The third capillary structure is disposed at a zone of the inner surface of the first plate, the zone is within a projection of the heat source projected onto the inner surface, and an area of the zone is smaller than an area of the projection of the heat source.