Wire's bending in wire electrical discharges machining is inherent error. It always exists because the forces were born in machining, creating the vibration of wire, making the wire slower than wire's guide. Thus, it created decrease in dimension and shape accuracy, wire's rupture. With improvement of the machining accuracy, the determination of wire's bending very important. In this paper, the authors introduce how to find of wire's bending, declare the relation between workpiece's height ant wire's bending when machining 45 steel in DK7732 WEDM machine.