Corrosion and high temperature are two main detrimental factors that degenerate the mechanical properties and lead to decrease both in strength and durability of steel. The combined influence of corrosion and high temperature on the mechanical properties of grade D36 marine steel is proposed in this study. A series of tests were conducted to determine the post-fire mechanical properties of corroded marine steel. Specimens were corroded by a saltspray test, and then heated to 500 °C or 900 °C. Afterward, stress–strain curves, elastic modulus, yield stress and ultimate strength of the specimens were obtained from tensile coupon tests. Three-dimensional laser scanning was used to evaluate the impact of corrosion. The microstructure and fracture morphology analyses were carried out by metallographic microscope and scanning electron microscope (SEM), respectively. It was found that corrosion and high temperature have significant influence not only on the mechanical properties, but also on the microstructures and corresponding fracture morphology of grade D36 marine steel.