The invention provides a double-layer low level vacuum preloading consolidation device and a soft soil foundation consolidation method. The device consists of a main controller, a power distribution controller, a vacuum pump, a submersible pump, a buffer knockout drum, a control valve, a vacuum gauge, a vacuum degree detecting head, a hydraulic fill consolidation layer vacuum pipe network, a soft soil consolidation layer vacuum pipe network, a subsidence mark, an open water overflow port, pipes and gauge tables, wherein a cofferdam is reclaimed along the consolidation area border in the soft soil foundation, a soft soil consolidation layer is formed in the cofferdam, the soft soil consolidation layer is provided with the soft soil consolidation layer vacuum pipe network and a hydraulic fill consolidation layer, the hydraulic fill consolidation layer is provided with a bearing separation layer and the hydraulic fill consolidation layer vacuum pipe network, and the hydraulic fill consolidation layer vacuum pipe network is hydraulically filled with a sealing layer. The invention has the advantages of reasonable structure, convenient construction, short construction period, low cost, good consolidation effect, facilitation of construction in large areas, consolidation of the soft soil foundation, dredging, and reutilization of the dredged sludge after consolidation, and can solve the problem of difficult land occupation of a blow-off field and create economic benefits.