Using double-cladding structure we enhanced the coupling efficiency and power of pump light,greatly decreased power density of pump light in fiber core,naturally suppressed the bleaching phenomenon.The high absorbable power ratio (pump efficiency) can also be kept by means of offset double cladding structure.Both theoretical analysis and experimental result confirm the feasibility and advantage of this structure.The coupling efficiency of 80 % and pump power dencity of 3.2 W/cm 2 were obtained.