On the basis of a continuum theory of compressive SmC* we shall investigate a nucleation of disclinations, under a DC electric field, accompanied with the layer relaxation phenomenon between a couple of antiparallel chevrons. From the two-dimensional analyses of the layer structures and the c-director configuration with a screw disclination between a couple of anti-parallel chevrons, it is found that a screw disclination, which move depending on the applied electric field strength, may be produced under a certain electric field, and that such threshold field strengths critically depend on the molecular tilt angle, the cell thickness and an elastic constant. In addition one finds that there also exists a threshold for the layer reversal under a relatively high electric field.