The identification and design of the roll axis servo system with a small journey range in an airborne three-axis gyro body-stabilized platform were discussed and researched by time domain and frequency domain methods. The identification method based on the genetic algorithm was presented by the time domain method and the genetic algorithm was also discussed.Moreover, the opened-loop frequency characteristics of the system were obtained according to the closed-loop frequency characteristic measuring data by the frequency domain method.These methods resolve the difficulty of roll axis servo systems with small journey range in directly measuring opened-loop frequency characteristics. On the basis of the transfer function identified, the control system corrected can meet expected indicators. Experimental results prove that the identification can nicely describe characteristics of the proposed system even in big noises, shorter journey ranges and poor measuring conditions. The closed-loop bandwidth of control system is 121 rad/s and the stability margin is 60° after correcting, which can meet the indicators of an engineer.