It is theoretically found that phase locking high-order lateral modes of laser diode array (LDA) with a short external cavity can be realized. The far field pattern, which comprises a main lobe and side lobes, is observed for a LDA positioned in a short external cavity. There are structures composed of peaks and valleys, symbolizing phase locking, within the side lobes. From these results, it can be concluded that the phase locking of high-order lateral modes of LDA exists when the external cavity is short enough.