The invention, belongs to the field of wastewater treatment technology, is a two-phase anaerobic reactor enhanced by addition of zero valent iron (ZVI). In the reactor, 2˜4 ZVI-filling layers are settled in the middle of the anaerobic hydrolysis-acidification tank, the effluent of which is fed into the rear anaerobic methanogenic tank. The degradation of organics is effectively enhanced in the anaerobic hydrolysis-acidification tank with dosing of ZVI, which may produce more acetic acid that is a desired substrate for the subsequent methanogenesis. Meanwhile, the acidic environment of the hydrolysis-acidification tank is helpful for the dissolution of ZVI to maintain its activity. The reactor is reasonably designed with high performance and strong shock resistance in anaerobic treatment of various wastewaters. Tests in lab-scale showed that hydrolysis-acidification and methanogenesis in this combined system were significantly improved compared with a reference reactor without addition of ZVI.