The invention discloses an A/O type film-free biological cathode microbial fuel cell, which relates to the field of an electrochemical energy resource and aims to solve the problems that the microbial fuel cell is high in construction and operation cost and is not suitable for practical application because a heavy metal catalytic material and an electronic transfer mediator are required to be added for an anode chamber and a cathode chamber of the traditional microbial fuel cell are separated by a proton exchange membrane. The anode chamber is arranged on a central part in the cathode chamber; two rows of transfer holes are uniformly drilled along the periphery on the side wall of the lower end of the anode chamber; granular activated carbon is filled in the anode chamber; one end of an anode carbon rod is inserted into an anode area; the distance between the lower end surface of a sieve tray and the bottom surface of the anode chamber is 10cm; the granular activated carbon is filled on the sieve tray; one end of a cathode carbon rod is inserted into a cathode area; the other end of the cathode carbon rod is connected with the other end of the cathode carbon rod through a copper lead; and an aerating head is arranged at the bottom of the cathode area and is connected with an air pump through a pipe. The A/O type film-free biological cathode microbial fuel cell is applied to microbial power generation or sewage treatment synchronous power generation.