By adding the thulium oxide nanoparticles ( NP) of Gd2O3 and Eu2O3 and Nd2O3 to polymer dispersed liquid crystals (PDLC), and the transmittances of PDLC and NP-PDLC changing with voltage in visible light was tested, and the thulium oxide modulation for PDLC was studied. The results show that transmittance of Gd2O3-NP-PDLC decreases with increasing voltage when the voltage is less than 10 V. The relaxation phenomenon of the sample appears at 15 V, and its transmittance curve fluctuates slightly around that at 10 V. The transmittance of Gd2O3-NP-PDLC increases rapidly at 20 V, and its filter phenomenon emerges. And the transmittance of Eu2O3-NP-PDLC decreases with increasing voltage, but the decrease is only slight. And the transmittance of Nd2O3-NP-PDLC changes with voltage insignificantly.