This work aims to study the galvanic corrosion, crevice corrosion and synergetic effect of TA2-Q235 couple in simulated seawater solution, which provides theoretical guidance for application of titanium steel composite plate in marine engineering structures and improves the service life of components. The anodic and cathodic polarization behavior of TA2 and Q235 during different corrosion forms were investigated through polarization curves and potential. The anodic dissolution rate of Q235 was measured by electrochemical workstation and corrosion mass loss. The corrosion degree of anodic metal and surface morphology of corrosion product were observed by optical microscope and SEM. The results indicated self-corrosion current density of Q235 in 3.5% NaCl solution was 35.5 μA/cm2 and it showed typical uniform corrosion. The coupled potential was close to the corrosion potential of Q235 and the average galvanic corrosion density of galvanic couple was 40.5 μA/cm2, which indicates the acceleration effect by TA2 on anodic dissolution of Q235 was light. There was no potential difference inside and outside crevice of Q235, which causes no galvanic current in the circuit. The cathodic reaction inside crevice was inhibited due to insufficient oxygen supply, resulting in less corrosion degree inside crevice than outside crevice. The morphology outside crevice was close to self-corrosion of Q235. The corrosion rate inside crevice of Q235 was lower than its self-corrosion under the synergetic effect of galvanic and crevice of TA2-Q235. The inhibition effect of oxygen depletion inside crevice on cathodic reaction of Q235 was stronger than the acceleration effect of TA2 galvanic effect on anodic reaction of Q235, which cause corrosion rate inside crevice of Q235 was lower than its self-corrosion.