We consider the one-dimensional problem of imperfections influence on the Purcell effect in photonic crystal system. We demonstrate that the presence of disorder in a one-dimensional photonic crystal can lead to a modification of the spontaneous emission rate in the photonic band gap (PBG) frequency region. We show that the amount of disorder regulates two different scenarios of the Purcell effect modification. In the case of weak disorder, the Purcell enhancement of the spontaneous emission occurs at PBG edges, and, in the case of strong disorder, it occurs at PBG centre.