A method for in-situ treatment of sediment simultaneous with microbial electricity generation is provided, comprising steps of constructing a microbial fuel cell, placing the microbial fuel cell in the sediment, forming a cell circuit, and cultivating microorganisms to generate electrical power. The method overcomes shortcomings found in the prior art and uses organics in the sediment as fuels to in-situ treat the sediment with simultaneous electricity generation. A device for implementing the method is also provided, which can be expanded in different directions as needed and is easy to maintain during long-term operation. The device has many advantages including compact structure, easy operation, low cost, high output power density, significant reduction in sediment COD, no influence on water flow, and environment-friendly.