The invention provides a testing device and method for cathode protection of an indoor ship body. The testing method comprises the following testing steps: 1 scaling down a ship body into a ship body model capable of being tested indoors; 2 determining materials and distribution positions of sacrificial anodes; 3 connecting the plurality of sacrificial anodes with the ship body model; 4 putting the ship body model into an experiment water groove and controlling a flow speed of seawater in the experiment water groove by an adjusting valve; 5 carrying out data acquisition on a cathode protective potential of the ship body model by utilizing a monitoring device under the conditions of different seawater flow speeds and different anode positions; and 6 analyzing monitored potential data by a computer and carrying out optimizing processing on the positions of the sacrificial anodes according to an analyzing result; and finally, providing a reasonable layout plan. According to the testing device and method for the cathode protection of the indoor ship body, a cathode protection effect of a ship under a real sea environment can be simulated and the sacrificial anodes distributed on the ship are monitored in real time; the problem that the cathode protection effect of the ship body is not ideal caused by unreasonable distribution of the sacrificial anodes is solved.