Coupled laser array, which realizes phase locking of elementary lasers with evanescent waves coupling, is a promising scheme to realize coherent beam combination. To reveal the stability of the phase-locked state in the array, the influence of the frequency drift on the phase dynamics of the two-coupled-laser array is researched. It is demonstrated that the frequency drift will break up the phase-locked state of the laser array and induce the spatial instability of the far-field intensity due to phase noise. It is also found that although the evanescent coupling between elementary lasers can restrain these effects to some extent, the restrainability is too limited to be effective when the frequency drift is relatively strong. It is suggested that some anti-jamming protections should be applied to the array, especially in the atrocious environment. Furthermore, the phase-locked state of the array is more sensitive to the low-frequency component of the frequency drift. Therefore, the protections should pay more attention to the low-frequency jamming.