In the arid and semi-arid parts of Xinjiang (China), jujube (Zizyphus jujube Mill) orchards are regularly intercropped with cotton. In 2016–2017, a field study was conducted to compare the species composition and infestation pressure of spider mites in local jujube trees under a cotton-jujube intercropping system and a jujube monocrop system. Our results showed that Tetranychus truncatus Ehara accounted for 94.2–98.5% of all spider mites in either cropping systems. Overall abundance of tree-inhabiting spider mites, including T. truncatus, in intercropped orchards was generally higher than in monocrop ones. Combining our work with earlier findings, we demonstrate how intercropping of cotton and jujube trees generally increases population levels of spider mites on either crop.