The microstructure and mechanical properties of Mg-2Zn-1.5Cu(at%) alloy were investigated by means of metallographic microscope, scanning electron microscopy, transmission electron microscopy, XRD phase analysis and mechanical properties test. The results show that the as-cast alloy has obvious element segregation, and the main second phase is MgCuZn phase; the mechanical properties of the alloy decrease when the temperature rises with the plasticity changes are significantly higher than the strength, and the fracture mode of the alloy also changes from intergranular fracture at low temperature to transgranular fracture at high temperature; at the same temperature, the steady-state creep rate of the alloy increases and the creep mechanism is transformed from grain boundary control to joint control of grain boundary and dislocation with the increase of the stress; at the same stress, there are orders of magnitude increase in the steady-state creep rate of the alloy with the increase of the temperature, and the creep activation energy decreases from 130 kJ/mol to 36.4 kJ/mol; the alloy reaches acceleration creep stage at 200℃~45MPa and occurs creep fracture with obvious transgranular fracture characteristics in the fracture position and a large number of dislocations along the base surface in the matrix. Part of these dislocations climb and the MgZnCu phase has the effect of slowing creep deformation.