The stress corrosion cracking （SCC） and corrosion fatigue (CF) behaviors of micro-arc oxidized (MAO) Mg-3Al-1Zn alloy were conducted in air and 3.5 wt.% Na2SO4 solution, and their relations were discussed. The corrosion properties of the MAO Mg-3Al-1Zn alloy were improved significantly. Compared with those of the Mg-3Al-1Zn substrate, the SCC and CF strengthes of the MAO Mg-3Al-1Zn alloy were both reduced only about 10 MPa slightly in air. In 3.5 wt.% Na2SO4 solution, the CF properties were still degraded, but the SCC properties of the MAO specimens were enhanced apparently, from 58.24 MPa to 202.08 MPa. It indicated that the mechanical properties (SCC and CF) were not always linearly related with the corrosion resistance of the material. It was ductile fracture for the SCC specimens in air, and it was cleavage fracture in 3.5 wt.% Na2SO4 solution. While they were cleavage fractures for CF specimens regardless of the environments. This was due to the effect of the corrosive environment and alternating cyclic loading, which accelerated the crack propagation process. It displayed that the surrounding environments and loading types could affect the fracture mechanism of the material.