Abstract: To suppress optical noise of signals in master oscillator power amplifier (MOPA) systems, an experimental study was conducted on the effects of input signal power and pump power on the transfer characteristics of optical noise of input signals in a 1550 nm single-frequency erbium-doped fiber amplifier (EDFA), based on gain dynamics theory. Furthermore, the relative intensity noise (RIN) characteristics of the fiber amplifier were analyzed and verified using gain dynamics. The results demonstrated that under the conditions of low residual pump power and minimal amplified spontaneous emission (ASE) intensity, the suppression ratio of input signal intensity noise transfer was proportional to the amplification gain. This indicated that the transfer of input signal intensity noise could be significantly suppressed while increasing the output power. By optimizing the powers of the input signal and pump, the RIN of the output laser below 10 kHz was suppressed. Specifically, a 6 dB suppression was achieved in the range of 1 Hz to 200 Hz by optimizing the input signal power, and a 10.5 dB suppression was attained in the range of 1 Hz to 250 Hz by optimizing the pump power. This study provides references for parameter optimization and noise suppression in fiber MOPA systems.