The change of microstructure and its influences on the micro-hardness and compression properties of Zr57Cu15.4Ni12.6Al10Nb5 bulk amorphous alloy with isothermal heat treatment have been studied by X-ray diffractometer, scanning electronic microscope, micro-hardness tester and compression experiment. It has been found that as the heating time increases, the crystallization temperature of the amorphous alloy will decrease. The phase decomposition and/or partial crystallization will cause the micro-hardness to increase and the compression strength to decrease rapidly, and make the fracture mode of amorphous alloys changing to that of crystalline alloys.