The dimensional accuracy of workpiece worsens because of thermal deformation by grinding heat. In this study, to reduce the dimensional error thermal deformation of workpiece during grinding process is calculated with developed simulation analysis method. In simulation, the heat inflow and outflow are calculated with comparing the measured temperature on the ground workpiece surface. The surface temperature can be obtained easier compared with the grinding force that used as the input of conventional simulation method. By using this new simulation method, it is confirmed that the thermal deformation of the workpiece correlates with workpiece surface temperature at steady starts. The outflow heat from workpiece has constant value even if the coolant flow increased.