To study the application of ZnO in photocatalysis, a composite of La-doped ZnO nanorods and Ag2CrO4 nanoparticles was prepared by hydrothermal and precipitation methods. At a fixed concentration, the volume of Ag+ precursor has a significant effect on the composition and structure of the composite. With the increase in the Ag+ source volume, the amount of Ag2CrO4 nanoparticles generated in the composite increases. When the volume of the Ag+ source exceeds some critical value, although the amount of Ag2CrO4 nanoparticles in the composite continues to increase, the quality of the crystals is lower. Both the content and crystal quality of Ag2CrO4 nanoparticles affect the photocatalytic properties of the composite. The introduction of additional oxygen vacancy defects in nanorods leads to the formation of more, and larger, Ag2CrO4 nanoparticles in the composite without degradation of crystal quality. Then, two dyes (methyl orange and methylene blue) were selected to examine the photocatalytic properties of the samples. The improvement of photocatalytic performance of the composite samples is realized by the separation of electron–hole pairs in both ZnO and Ag2CrO4 crystals. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.