Abstract: The allelopathy in real habitat was simulated, and the leaves of Solanum pseudocapsicum and 3 other toxic plants growing in the same habitat were selected as materials. The content and components of soluble sugar in the extracts were determined by indoor Petri dish method, anthrone colorimetry and gas chromatography-mass spectrometry(GC-MS). The effects of different concentrations of aqueous extracts of S. pseudocapsicum, Hedera nepalensis, Cirsium maackii and Eupatorium odoratum leaves on seed germination indexes of S. pseudocapsicum were studied. The results show that different concentrations of 4 plant extracts had inhibitory effects on the germination of S. pseudocapsicum seeds, and all the germination indexes of S. pseudocapsicum seeds were reduced. Extraction with 0.2 g/mL Hedera nepalensis var. si water has a maximum inhibitory effect of −20.52 on liquefaction sense, and the comprehensive germination rate, germination potential, germination index and vitality index were significantly different from those of the control group; the soluble sugar content of the four plant extracts of different concentrations increased with the increase of the extract concentration. The soluble sugar content of 0.2 g/ml Hedera nepalensis var. si aqueous extract was the highest, which was 1.53 ± 0.02 mg/g. With the increase of the soluble sugar content, the more obvious its inhibitory effect on seed germination was; the olefins dominated by neophydiene are the dominant components of S. pseudocapsicum, and H. nepalensis, and the olefins dominated by Darlene D are the dominant components of C. maackii, which accounted for 37.94%, 78.7% and 52.94% respectively, and 5-isopropyl-4,6-dimethyl-3,6,8-nonatriene-2-ol was the dominant components of the extract of E. odoratum that accounted for 63.28% of the all components. The inhibitory effect of the aqueous extracts of 4 toxic plants increased with the increase of concentration. The correlation analysis showed that soluble sugar was the main factor to inhibit the seed germination of S. pseudocapsicum.