La1-xMgxNi2.8Co0.7 (x=0.1, 0.3, 0.5) hydrogen storage alloy was synthesized by solid diffusion method. The microstructure of the alloy was analyzed by XRD when the content of Mg was changed. When x equaled to 0.3, there was relative much La2Ni7 phase in the alloy and the alloy exhibited better integrated electrochemical performance. Its maximum discharge capacity reached 355.4mAh/g and capacity retention after 50 cycles（S50）was 77.80%. The results showed the existence of La2Ni7 phase would be conductive to the integrated electrochemical performance of the alloy.