Based on Valley′s quasi-cw approximation,the writing and erasing of gratings in materials exhibiting bulk photovoltaic effect on illumination with short light pulses (such as ns pulses) is investigated.The expression of space-charge field is given out in the paper with two time constants τpa and τpb.When considering and not considering the photovoltaic effect,the diagrams of the two time constants as a function of irradiance in units of 1/(sτR) are the same.The energy required to erase a grating to 1/e of its initial value is also studied in the two cases and the two results are also the same.In the case of short light pulses irradiance,photovoltaic effect has no effect on the writing and erasing photorefractive gratings in the LiNbO3 crystal.