To provide reference for the cathodic protection of the anode in steel shell immersed tube, the anodic behavior of Al-Zn-In-Si-Ti-Sn sacrificial anode in diluted seawater/backfill stone was investigated. Electrochemical tests, such as potentiodynamic polarization curve and electrochemical impedance spectroscopy (EIS), were measured in diluted seawater/backfill stone. The galvanic current and mix potential of the anode in diluted seawater/backfill stone were tested by galvanic corrosion test, then the dissolution morphology of the anode was observed. Because the backfill stone can hinder the diffusion of Cl- and dissolved oxygen, the corrosion rate of Al-Zn-In-Si-Ti-Sn sacrificial in diluted seawater/backfill stone was significantly lower than that in diluted seawater. The anode and Q420C steel were coupled to conduct galvanic corrosion experiment, and the area ratio of anode and cathode was 1:30. The galvanic current of Al-Zn-In-Si-Ti-Sn sacrificial in diluted seawater/backfill stone environment was significantly lower than that in diluted sea water. In diluted seawater/backfill stone environment, the mix potential shifted positively and the dissolution morphology was seriously uneven.