Abstract: A all fiber amplifier system was demonstrated based on large modulus area doped with Yb3+ ions, which used a 975 nm pump. The system used the interaction between the pump and Yb3+ ion active fiber to generate a signal source. Signal source was semiconductor laser amplified single-frequency seed light. The system was optimized, optical devices were reasonably designed and built, and the beam inverse transmission was controled to reduce the nonlinear optical interference. 100 W signal source acted on the system, the master oscillator power amplifier(MOPA) of multistage Yb3+ doped optical amplifier was adopted, the signal output 3.2 kW continuous laser. The average optical-to-optical conversion efficiency was about 78.26%. Output beam quality Mx21.657, My21.735. Output stability was less than 2%. The system continuous signal amplification output beam had a wide range of applications. The ytterbium doped ions all-fiber amplifier is mainly used in laser detection, industry measurement technology research, etc.