An immobilized microbial agent for in situ restoration of contaminated sediments, composed of Hangjin clay 2 #-loaded conductive microorganisms, obtained by the following methods: 1) pretreating Hangjin clay 2 # to obtain particulate filler; 2) amplification culture of conductive microorganisms to a bacterial liquid to be inoculated, and adding the Hangjin clay 2 # pretreated in step 1 in a certain ratio, mixing under anaerobic conditions, removing the supernatant after standing, and obtaining the immobilized microbial agent; the conductive microorganisms are Geobacter sulfurreducens, Geobacter metallireducens and Shewanella. The invention also discloses a method for preparing the immobilized microbial agent and the application of in situ restoration of contaminated sediments.