We innovatively synthesize multifunctional copolymers to change the surface polarity of PbS quantum dots. The original oleylamine ligands are replaced by carboxyl terminus, as carboxylcontaining ligands have stronger binding affinity towards the PbS quantum dots surface than aminebased ligands. After ligand exchange, PbS quantum dots are transferred from nonpolar solvent to polar solvent. The new mothod could keep the fluorescence efficiency and stability of PbS quantum dots in polar solvent better. Alcoholic solution of PbS quantum dots are coated on the surface of the tapered singlemode fiber by grow method to make fiber amplifier. Since fluorinecontaining polymers can affect the gain characteristics of the optical fiber amplifier, we study the influence of polymers with different fluorine content on the signal gain. The result shows that the signal gain are higher with increasing the fluorine content of the polymer.