With the vigorous development of aerospace technology, space communications, especially microwave optical transmission systems, require high-power, high-efficiency lasers and amplifiers to meet the requirements of high speed, large capacity and long transmission distance in space communications. The inter-satellite microwave photonics subsystem transmits the microwave signal to another satellite by modulating the microwave signal to the laser. The signal loss is very large after long-distance transmission. It is necessary to use a fiber amplifier as a preamplifier to improve the signal-to-noise ratio. The conversion efficiency of the fiber amplifier is a key performance index, which is related to the power efficiency, heat dissipation and weight of the entire laser amplifier. Aiming at the space application of optical fiber amplifiers, the design and experimental research of optical fiber amplifiers with compact structure, high output power and low power consumption have been carried out. In the electrical design, a semiconductor laser drive system with a digital signal processing chip as the core processor is designed, and a closed-loop control logic of output-detection-re-output is formed. Through automatic power control, the stability of the output power of the pump laser is ensured, the power consumption of the pump source during idle time is reduced, and the electro-optical efficiency is improved. The drive system is equipped with a temperature sensor and a semiconductor cooler to monitor temperature data in real time, and the semiconductor cooler will maintain the temperature stability of the pump laser. The powers of the input signal light and the output signal light can be obtained by two photodetectors, and the real-time sampling and comparison algorithm realize the automatic standby system when there is no input, and maintain the minimum power consumption operation. The mechanical design adopts photoelectric separation and modular design. Taking into account the temperature-sensitive characteristics of semiconductor lasers and the particularity of heat dissipation in the space, the optical part and the electronic part are respectively integrated in different spaces. The heat pipe in the heat dissipation layer will transfer the heat generated to the external heat treatment equipment, so that all devices do not need to consider too much heat dissipation space or add the heat sink, keeping the overall structure compact and small, and maintaining good heat distribution. The integrated design reduces fixed parts and keeps the overall weight below 1 kg. The optical structure adopts a two-stage amplification structure design, and the signal light is amplified through the erbium-doped fiber and erbium-ytterbium co-doped fiber, so that high power output can be maintained while maintaining a high signal-to-noise ratio. Furthermore, this paper studies the output performance of the entire system under different pump powers, and compares the conversion efficiency, power consumption and spectral characteristics of the amplifier under different fiber lengths. In order to obtain a good gain and signal-to-noise ratio, an 18 m long erbium-doped fiber and a 7.5 m erbium-ytterbium co-doped fiber are selected, the output spectrum of the signal light after the two stages are analyzed. Finally, the 1 551 nm milliwatt seed light is amplified to a 7.39 W signal output, and the signal-to-noise ratio is maintained at 40 dB. The output beam quality is 1.05, and the overall power consumption does not exceed 80 W. In this work, all the optical designs use polarization-maintaining devices, and the polarization extinction ratio of the fiber amplifier is 17.5 dB. The computer can be used to change the injection current of the pump source, thereby changing the final output power. All the modules can be specially adjusted according to the environment, and can be flexibly used in various occasions. This compact fiber amplifier is 20 cm long, 14 cm wide and 4 cm high, which is very suitable for space laser communication.