The invention relates to the field of wood vinegar, and particularly discloses a preparation system and method for low concentration wood vinegar for environmental protection use. The system comprisesa loading system which transports garden waste materials, an extraction system which is connected to the loading system and conducts distillation treatment on the materials conveyed by the loading system to obtain a pyrolysis gas, a cooling absorption system which is connected to the extraction system and conducts four-stage spray cooling absorption treatment on the pyrolysis gas to obtain a crude wood vinegar product and a separating impurity removal system is connected to the cooling absorption system to physically separate the wood vinegar crude product and remove impurities and simultaneously supplies circulating water for the cooling absorption system. The system uses garden waste as a raw material to prepare a wood vinegar liquid product by a low-temperature anaerobic combustion method, the pyrolyzed biomass is used as a system fuel, only a small amount of additional gas or electric energy and the like is needed, and a cost is saved.