Voltage control of electromagnetically induced grating is studied in an asymmetric double quantum dot system by use of quantum coherence in semiconductors. Owing to voltage tunneling effect, electromagnetically induced transparency can appear synchronously at two different frequency windows. By suitably tuning related parameters, the absorption property can be significantly modified. Therefore the intensity of a phase grating, especially its first-order diffraction intensity, can be enhanced significantly for a certain probe detuning with weak absorption. The influences of tunneling voltage, intensity of the pump field, interaction length and others on the efficiency of phase grating are investigated and the results show that the first-order diffraction efficiency of the phase grating is enhanced by 50% by simultaneously increasing the voltage tunneling rate and intensity of pump field. The results have potential applications in quantum information processing, quantum networks and optical imaging.