A planar waveguide array, whose structure is similar to a volume phase grating,can be fabricated in a congruent SBN:Cr (Sr0.61Ba0.39Nb2O6:Cr) crystal by irradiation of two-beam interference pattern,and,simultaneously, by applying an appropriate direct electrical field along the c-axis of the crystal. The transversal index profile of the waveguide array is measured in real-time using a Mach-Zehnder interferometer,and the maximum index change in the waveguide region is close to 10-4. The initial guiding tests show that it is feasible to write a dynamic planar waveguide array in the SBN:Cr crystal by using irradiation of period structure-light,due to the rapid response property of SBN:Cr crystals. And the dynamic control of the waveg uide can be realized by switching the writing lights on or off,or adjusting the angle of the two interferent beams. Moreover,the waveguide parameter such as the index profile in the waveguide zone can be effectively controlled by varying the external electric field.