By adjusting experimental parameters, such as reaction time and ratios, CeO2/CePO4 composites have been prepared through a single-step hydrothermal process, in which CeO2 octahedra and CePO4 nanowires mingled with each other to form many interfaces. The formation of the particular structure can be explained by heterogeneous nucleation theory: the existed CePO4 nanowires at the early stage of hydrothermal process provide many thermodynamically favorable sites, on which the nucleation energy of octahedral CeO2 is the lowest. The photoluminescent (PL) properties of CeO2/CePO4 composites showed that the strongest PL emission can be achieved with initial Ce/P of 4 and hydrothermal time of 24 h. And final Ce/P of the samples at this point was the maximum value by the EDS analysis. So it was proposed that the interaction between more CeO2 and the more coatings of CeO2 to CePO4 are responsible for the best PL properties.