Abstract: Mirabilis jalapa, an alien invasive plant, can accumulate cadmium (Cd) and exert allelopathic effects to other plants. The detected sterols in M. jalapa will significantly affect seed germination and seedling growth of other plants. Although the allelopathic effects of M. jalapa on crops without heavy metal have been reported, few studies focus on the allelopathic effects in the coexistence of Cd. A hydroponic experiment was conducted at different Cd concentrations to determine the allelopathic effects of root exudates from M. jalapa on soybean and maize, the content of β-sitosterol in different parts of M. jalapa and its root exudates, and the allelopathic effects of exogenous β-sitosterol with different concentration (0, 0.125, 0.5, 1, 2 mg·L^-1) on soybean and maize. The results show that with Cd stress, the allelopathic inhibition effect of root exudates from M. jalapa on soybean was stronger than that on maize. The content of β-sitosterol in the roots of M. jalapa was significantly higher than that in the stems and leaves. The content of β-sitosterol in the roots significantly reduced at high Cd concentration, while the content of β-sitosterol in the root exudates significantly increased. The seed germination and seedling growth of soybean and maize were significantly inhibited at the addition of 0.125 mg·L^-1 β-sitosterol, but the seedling growth of maize was promoted by the addition of other concentrations of β-sitosterol. The seed germination and seedling growth of soybean were inhibited with different allelopathic degree. With the increasing concentration of β-sitosterol, the activities of superoxide dismutase (SOD) and peroxidase (POD) in leaves of soybean seedlings were firstly increased but then decreased. The content of malondialdehyde (MDA, a product of cell membrane lipid peroxidation) in soybean leaves was significantly higher than that of the control at the addition of 0.125 mg·L^-1 β-sitosterol. However, the variation of MDA content in maize leaves was not significant. Comparatively, the activities of SOD and CAT in leaves of maize was increased. At low or high β-sitosterol concentration, the chlorophyll a and carotenoid contents in the leaves of the two crops were significantly decreased compared with the control. At Cd stress, the allelopathic inhibition of β-sitosterol on soybean was higher than that on maize. Therefore, the remediation of Cd-polluted soil by the intercropping of maize and M. jalapa is feasible.