Using a light ray tracing, this paper presents the matrix expression for an electrooptic deflector. It is the extension of the famous ABCD matrix expression for Gaussianoptics, but includes the possibility of considering a time-dependent element for the deflector.A Pulse shaping system is studied with theory of matrix optics, which is constructed mainlyby a pair of deflectors. Finally make demands on the accordance of two deflectors'parameters, synchronization precision between electronical pulses added to the deflectors, and positions of the deflectors in the pulse shaping system are presented.