Ultra-short optical pulse source is one of key components in optical time-division multiplexing(OTDM) system. In this paper, a wavelength and repetition rato tunable actively mode-locked fiber ring laser based on cross-gain modulation in a reflective Semiconductor Optical Amplifier(SOA) is demonstrated. Theoretical model for this scheme is also established and output characteristics are calculated. Stable picosecond pulse trains with high extinction ratio at 10—40 GHz repetition rato are obtained. 30nm wavelength tuning range is also achieved in our proposed actively mode-locked laser.