A theoretical analysis is given about the relationship between clock frequency components and pulse amplitude for unequal-amplitude even-multiplexed OTDM (Optical Time Division Multiplexing) signals, and physical mechanism of clock recovery based on SOA (Semiconductor Optical Amplifier) mode-locked fiber laser is demonstrated from the point of time domain and frequency domain respectively. In experiment, 2.5 GHz frame clock and 20 GHz bit clock are extracted from unequal-amplitude even-multiplexed 8×2.5 GHz signals by using SOA mode-locked fiber laser. The extracted clock pulses have several desirable features such as low timing jitter, broad wavelength tuning range and polarization independence. This technique can be applied to clock recovery in high-speed OTDM network.