Cast-in-situ concrete suffers complicated working conditions in sulfate-rich saline soil areas. Sulfate-magnesium combined attack can be encountered in heavy saline or salty lake areas. This study investigated the degradation process and corresponding mechanisms of cast-in-situconcrete, contaminated by chlorides, partially exposed to sulfate-magnesium combined corrosiveenvironments. Concrete samples were cast and partially immersed in the pre-prepareddistilled water, sulfate or sulfate-magnesium mixed solutions for 12 months. Physical andmechanical properties of concrete samples were continuously measured and recorded duringthe immersion. Sulfate concentration in different depths were measured by chemical titration. SEM, XRD, TG/DTG tests were conducted to analyze the microstructural and mineral propertychanges after corrosion for concrete suffered different corrosion conditions. Results show thatpartially immersed concrete encounters both chemical and physical degradation induced bycorrosive sources. Concrete contaminated by chlorides obviously shows weaker resistanceagainst sulfate attack and the strength development is also negatively affected. Magnesium inthe environments reduces the early strength of partially immersed cast-in-situ concrete whileenhancing the sulfate resistance ability in the later corrosion stage. Magnesium limits thenegative effect of contaminated chlorides on the partially immersed cast-in-situ concrete. Performance of cast-in-situ concrete is different from precast concrete when encounteringdifferent corrosive sources, and thus more attention should be paid on the degradation ofcast-in-situ concrete structures induce by aggressive environments.