A micro-current electrolysis-sterilization-algaecide device includes the solution conductivity detector installed in the inlet pipe of the tank, at least a group of electrodes set in the tank in accordance with the order of anode, auxiliary electrode, and cathode, and the controller, which judges the conductance values, controls the electrode polarity and the circuit connections. Said controller includes judging unit to determine the conductance values of water, and according to the results to trigger the corresponding seawater electrolysis-model unit, the fresh water electrolysis-model unit, or the pole-reversing electrolysis-model unit. The device can be used to the seawater and fresh water sterilization algaecide, with good bactericidal algaecide effect, automatic scaling, and a wide range of applications. By adding ultrasonic generator, the device can destroy a variety of bacteria and algae cells. Said device has a simple structure and a wide range of use.