The deformation mechanism of the spray formed 70Si30Al alloy was studied by hot compression on a Gleeble-1500 test machine.It is shown that hot deformation of the spray formed 70Si30Al alloy is achieved by liquid flow due to isostatic pressure and movement of solid particles due to shear force.Deformation condition depends on the nucleation rate and closure rate of the cavities. The flow stress slightly varies when the difference between the nucleation rate and closure rate of the cavities is small;however,it decreases when the nucleation rate of the cavities is greater than the closure rate of the cavities.