We report a technique for continuous tuning the coherence length of semiconductor laser. The coherence length of the semiconductor laser is controlled by using optical feedback scheme. The results show that the coherence length of semiconductor laser can be shortened from several meters of the original solitary laser to 100 μm by the implementation of optical feedback. Experimental results indicate that the coherence length of the laser depends strongly on the feedback strength， but is insensitive to the bias current. The results of numerical simulations using rate equation of semiconductor laser are fully consistent with our experimental results.