To study high precision external modulation characteristics of high speed 1550 nm microwave fiber link, the relation of output power, threshold current and temperature is disucssed based on the physical model of multiple quantum well-distributed feedback (MQW-DFB) laser diode (LD). A corresponding power and temperature control circuit is set up to ensure the output optical power fluctuation within ±0.005 dB and the modulated output with 0.5 nm of 3 dB spectrum width. Its side modes are planar and the side mode suppression ratio is more than 30 dB. In addition, the automatic gain control circuit and accessional phase modulation circuit are designed in order to control light power on the stage of external modulation. Experimental results shows that the external modulation microwave fiber link system composed 1550 nm MQW-DFB laser diode and corresponding driving circuits can effectively improve output light power stability of light emitting module. It overcomes the disadvantages of light spectrum expansion and unstable optical extinction ratio due to direct modulation and realizes fiber transmission of microwave signal with high linearity and low distortion.