The formulas of reflectivity were derived in one-dimensional holographic photonic crystals with the method of the transfer matrix. With this method, the reflectivity of the one-dimensional holographic photonic crystals was calculated when the basic period of the refractive index modulation and the optical thickness of the basic period structure of the photonic crystal changed. The results show that the width of the gap decreases and the gap center position moves to short wave with the increasing of the parameters of the basic period of the refractive index modulation. With the increasing of the optical thickness, the width of the gap increases, the center position of the gap moves to long wave. When the photonic crystals are designed, the control of the photonic band gap can be achieved via changing the basic period structure parameters of the photonic crystals.