In order to improve the amplification performance of the fiber Raman amplifier,a photonic crystal fiber with high Raman gain coefficient and larger negative dispersion was designed.The full vector finite element analysis method is used to numerically analyze the photonic crystal fiber with a regular octagonal cladding,explore the effects of changes in air pore structure and core doped germanium concentration on effective mode field area and Raman gain coefficient.Finally,a photonic crystal fiber with small mode field area,high Raman gain coefficient and large negative dispersion is obtained.The research results show that the germanium-doped photonic crystal fiber structure with a cladding air hole diameter of 1 μm and a hole spacing of 1.2 μm at a pump wavelength of 1 450 nm and a signal wavelength of 1 550 nm can obtain a high Raman gain coefficient of 19.97 W－1·km－1.At the same time,a large negative dispersion of －327.6 ps/(nm·km) can be obtained at 1 550 nm.The comprehensive characteristics of this fiber are of great significance to the improvement of the amplification performance of the Raman amplifier.