Abstract: In this paper, the law that the color of the twisted nematic liquid crystal cell changes with the voltage is studied. It is found that when the polarizer and analyzer is at a 35 degree angle and the liquid crystal cell is in the case of no electric field,the polarized light interference color presents the light red. After the voltage reaches 1.8V the liquid crystal presents green,blue and red et al in turn,and when the voltage reaches saturation voltage 3.1V the liquid crystal cell would present no color. The reason of the phenomenon is analyzed by using the principle of polarization interference.