In order to accurately measure the Plank constant and realize quantum mass standard by means of joule balance,a laser interferometric displacement measurement system,which consists of three laser heterodyne interferometers and a folded Fabry-Perot(F-P) interferometer using absolute distance measurement,measures the displacement of the mutual inductance coil in joule balance moving along the vertical direction in the uniform and radial magnetic field.The displacement of the center of mass and the gesture of the moving coil are obtained through three laser heterodyne interferometers with less than 10 nm uncertainty,and the designed Fabry-perot interferometer would be applied to compare and calibrate the nonlinearities of one heterodyne interferometer.The simulation results show that this method has the displacement measurement range of about 30 mm and the resolution of less than 1 nm.It will be the potential method achieving the relative uncertainty of 1.0×10-9 for the displacement measurement of the moving coil in a vacuum.