The invention discloses a composite steel bar corrosion inhibitor for a marine environment and an application thereof. The corrosion inhibitor comprises the following components: 100-120 g/m<3> of sodium molybdate, 1-2 g/m<3> of d-sodium gluconate, 2-3 L/m<3> of diethanol amine, and 1-2 L/m<3> of petroleum sodium sulfonate; the content of the components is based on the amount of the reinforced concrete to be prepared. The corrosion inhibition efficiency of the corrosion inhibitor disclosed by the invention is always greater than 95%; the corrosion inhibitor has the advantages of long acting, good corrosion inhibition effect, readily available materials, environmental friendliness, low use concentration, low cost and the like, and is a promising concrete reinforcement corrosion inhibitor suitable for the marine environment.