This paper presents the experimental and numerical investigations on the axial compression behavior of Q690 high-strength steel welded I-section columns with corrosion pits. Firstly, a series of axial compression tests were performed on the column specimens with regularly distributed machining pits. A numerical study with consideration of the randomness of corrosion pits was then carried out. The results revealed that corrosion pits changed the failure mode of the column, and led to significant degradation of ultimate resistance, even reaching 40.4% when the pitting volume ratio is only 15%. Finally, the equivalent residual plate thickness was defined and adopted in the codified approaches for determining the residual resistance of such members.