The invention discloses a high-stability volume-expanded type chassis of a caravan carriage. The high-stability volume-expanded type chassis comprises an upper chassis, a lower chassis and a movable chassis, wherein the structure of the upper chassis, the lower chassis and the movable chassis and the assembly relation of the upper chassis, the lower chassis and the movable chassis are arranged, so that under the premise that the chassis does not cause any interference to any article above the chassis, the purpose of expanding the volume of the chassis is realized; when the movable chassis is under a sliding-in state, the movable chassis and landing legs mounted on the movable chassis are all retracted between the upper chassis and the lower chassis; and when the movable chassis is under a sliding-out state, the landing legs folded below the movable chassis are opened, so that the landing legs are used for supporting the movable chassis.