In order to improve the amplification performance of the fiber Raman amplifier,a photonic crystal fiber with high Raman gain coefficient and larger negative disp ersion 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 ar ea 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 r esults show that the germanium-doped photonic crystal fiber structure with a cladding air h ole diameter of 1μm and a hole spacing of 1.2μm at a pump wavelength of 1 450nm and a signal wavelength of 1550nm can obtain a high Raman gain coefficien t of 19.97W－1·km－1.At the same time,a large negative dispersion of －327.6ps/(nm·km) can be obtained at 1550nm.The comprehensive characteristics of this fiber are of great significance to the improvement of the amplification performance of the Raman amplifier.