The high power semiconductor lasers were side－mode injection locked with freque ncy difference 1300?GHz with respect to its free working frequency using inject ion locking technique.The transfer of coherent characteristic between the master laser and slave laser was studied experimentally in detail by using saturated a bsorption spectra and optical heterodyne technique.The relation of locking bandw idth versus the ratio of injection power and the mode building process of inject ion locking were measured　and the experimental locking bandwidth agreed with the side－mode locking bandwidth obtained by multi－mode rate equation followed by injection term.The threshold injection light power for realizing side－mode inje ction locking was calculated theortically and tested by experiment.