A scheme of all-optical clock extraction based on injection locked semiconductor laser is proposed and demonstrated. In the scheme, optical carrier and one clock component of return-to-zero (RZ) signal lock two semiconductor lasers to obtain the phase locked optical outputs. When these two components are coupled together, the recovery clock signal is achieved. Two distributed feedback (DFB) lasers are used to extract the clock signal of a 10 Gb/s RZ signal experimentally. This scheme is very flexible in dynamic range of injected power, tunability and stability requirements of signal wavelength. This novel technique also has potential in integration and practicability.