Wire saw has a unique benefit in cutting precious material like SiC, Si monocrystal and gem etc since the cutting force is small, and the kerf loss is low and so on. In the common wire saw cutting process, the production efficiency is low, the wire saw wear is dramatic severe, the surface roughness of part is not expected and collapses flaws often occur on wafer as well, all those problems have a heavy effectiveness on wafer quality. In order to solve those problem, the ultrasonic vibration machining (UVM) has been applied to cut the hard & brittle materials which has a significant improvement on surface integrity of wafer and increasingly apply to nonconductive materials cutting, such as glass, ceramics, Si, gem and so on. In this paper, the cutting force for SiC monocrystal wafer by wire saw with UVM is studied, the mathematic model of cutting force for wire saw with UVM is discussed and the Fourier series expansion is used to solve the equation of cutting force. The experiments that the process parameters influence on the cutting force by common wire saw cutting and wire saw with UVM are conducted, respectively. The result show that wire saw with UVM can significantly decrease the cutting force, which is consistent with the theoretical analysis.