The mirid, Lygus pratensis (L.) (Hemiptera: Miridae), is a major pest of cotton (Gossypium spp.) in Xinjiang Uyghur Autonomous Region, China. In this study, we aimed to reveal the preferences of L. pratensis toward four potential trap crop plants for use in controlling this pest. The population densities of L. pratensis on five host plants were investigated by visual observation, and the behavioral responses of L. pratensis to the five host plants were determined by Y-type olfactory assays and laboratory selectivity assays. The results showed significant differences in host preferences in the field. The average numbers of adults on the five host plants are in the following order, from high to low: Lepidium latifolium (L.), Kochia prostrata (L.) Schrad, Chenopodium glaucum (L.), Medicago sativa (L.), and Gossypium spp. Laboratory selectivity assays found that K. prostrata had the highest number of adults at 5 min, but L. latifolium had the highest number of adults from 1.5 to 4.5 h. The Y-tube olfactometer assays found no significant evidence for selection of L. pratensis between the volatiles of M. sativa and pure air, but did for the other four plants. In conclusion, the blooming stage of L. latifolium was the most attractive to L. pratensis in the field and is, thus, a potential trap crop plant for L. pratensis.