Stress corrosion cracking (SCC) behaviors of Mg-7Al-0.3Mn alloy in 0.21M K2CrO4+0.6M NaCl solution and in air were studied using slow strain rate test (SSRT). The effect of electrode potential on SCC behaviors of the alloy was investigated in 0.21M K2CrO4+0.6M NaCl solution during SSRT. The fractographs of the alloy tested in air and in the solution were observed. These results indicated that SCC of the alloy was related to the hydrogen embrittlement and pitting corrosion. The pitting corrosion was the cause of crack initiation, and the hydrogen embrittlement leaded to crack propagation.