To screen the straw of Solanum spp. for improving the phytoremediation ability of cadmium (Cd) hyperaccumulator plants, a pot experiment was conducted in this study by adding straws from four Solanum species (Solanum alatum, Solanum photeinocarpum, Solanum nigrum var humile, and Solanum nigrum) into the Cd-contaminated soil for planting the potential Cd-hyperaccumulator Solanum diphyllum, and the effects of Solanum spp. straw on the Cd accumulation of S. diphyllum were studied. Compared to the control (no straw apply), only S. alatum straw increased the shoot biomass of S. diphyllum, while other straw samples decreased. The straw of S. alatum increased the chlorophyll a and total chlorophyll contents in S. diphyllum. In contrast, the straws of S. alatum, S. photeinocarpum, and S. nigrum var. humile increased chlorophyll b and carotenoid contents. Meanwhile, the straws of the four Solanum spp. did not affect or reduce the superoxide dismutase activity of S. diphyllum, while they enhanced the peroxidase and catalase activity and protein content to some extent. The straws of S. alatum, S. photeinocarpum, S. nigrum var humile, and S. nigrum decreased the shoot Cd content in S. diphyllum by 20.82%, 30.90%, 17.13%, and 16.19%, respectively, compared to the control; they also decreased the Cd extraction by shoots. These observations together indicate that the straw of Solanum spp. reduces the phytoremediation ability of S. diphyllum and cannot be used for Cd-contaminated soils.