Abstract: Phase locking of a diode laser array in an external Talbot cavity was studied. Far field distributions of in-phase mode and out-of-phase mode were calculated using Fresnel diffraction formula of one-dimension on the basis of near field amplitude distribution. According to the distributions of the in-phase mode and out-of-phase mode in fraction Talbot cavity, a tilted external cavity mirror of 1/2 Talbot cavity was adopted, which made the in-phase mode be selected and the loss of the mode be lowered. In order to let the feedback light be injected into the elements effectively in this experiment, a “sandwich” construction of composite diamond is utilized to package the diode laser array which has obviously eliminated the “smile” effect. Phase locking of in-phase mode is obtained in the e