A series of novel polyfluorene derivatives P1/4, P2/4, and P3/4, containing phenanthro[9,10-d]imidazole group on backbone are designed, synthesized, and well characterized. They all show high-molecular weights, good solubilities, and excellent thermal stabilities. The CV results of all three compounds show the lower LUMO levels and higher HOMO levels than PF. Among them, P3/4 exhibits deep blue emission both in solution and in solid state. The PLED based on P3/4 shows higher device performance and locates in the deep blue region with a CIE coordinate of (0.17, 0.08).