The growth of heterogeneous crystal has aroused a great deal of interest in recent years. In this study, KH_2PO_4(KDP)/KTaO_3(KT) heterogeneous crystal is acquired based on the KT substrate. Here, we report the observation of the oriented layer-by-layer structure in KDP/KT composite crystal by scanning electron microscopy(SEM). The structure of KDP/KT composite crystal is accurately identified by transmission electron microscopy(TEM) for the first time and we find that the KT crystals dope into KDP crystal in the growth process with the mode of doping. It can be obtained from the analysis of crystal structure that the structure difference leads to the doping growth mode. Our research demonstrates a facile method to fabricate a composite nonlinear optical crystal based on KDP/KT heterostructure, and might shed light on potential applications of the composite nonlinear optical crystal. In this study, KH_2PO_4 (KDP) / KTaO_3 (KT) heterogeneous crystal is acquired based on the KT substrate. Here, we report the observation of the oriented layer- by-layer structure in KDP / KT composite crystal by scanning electron microscopy (SEM). The structure of KDP / KT composite crystal is accurately identified by transmission electron microscopy (TEM) for the first time and we find that the KT crystals dope into KDP crystal in the growth process with the mode of doping. It can be obtained from the analysis of crystal structure that the structure difference leads to the doping growth mode. Our research demonstrates a facile method to fabricate a composite nonlinear optical crystal based on KDP / KT heterostructure, and might shed light on potential applications of the composite nonlinear optical crystal.