A kind of optical fiber doped with CdSe/ZnS quantum dot in low concentrations was fabricated for preparing a fiber amplifier. The photoluminescence and absorption spectra transmitted through the doped fiber were measured in different doping concentrations and fiber lengths. Effects of the doping concentration and fiber length on the spectra were investigated by the experiment. Compare with the doping before, a red shift of the photoluminescence-peak wavelength was observed after the doping. The red shift goes up with the increases of doping concentration and fiber length in the concentration ranging from (0.33 ~ 2.5) times 10-2 mg/mL and the fiber length from 1-20 cm. For the given excitation intensity, the maximum PL-peak intensity is related to the fiber length, and in the given fiber length, it is related to the doping concentration.