In recent years, there have been many studies on the response of plants to heavy metal stress, but the metabolic changes in bryophytes, pioneer plants quickly responding to environmental changes, under exogenous cadmium (Cd) stress have yet to be explored. In this indoor experiment, the responses in the metabolome of bryophyte Tortella tortuosa (Hedw.) Limpr. to different Cd exposure levels (0 (CK), 5 (T1), and 10 (T2) mg·L⁻¹) were analyzed. The results showed that the number of differentially accumulated metabolites (DAMs) secreted by T. tortuosa increased with the increase in the Cd concentration, and the biosynthesis of cofactors, D-Amino acid metabolism, Arginine biosynthesis, ATP-binding cassette transporters (ABC transporters), and biosynthesis of alkaloids derived from shikimate pathway were the main pathways enriched by DAMs. The relative abundances of malic acid, N-Formylkynurenine, L-Glutamine, L-Histidine, LL-2,6-Diaminopimelic acid, and fusaric acid in the T2 treatment increased by 16.06%, 62.51%, 14.51%, 11.92%, 21.37%, and 35.79%, respectively (p < 0.05), compared with those of the CK, and the correlation analysis results showed that the above DAMs were closely related to the changes in plant antioxidant enzyme activity and Cd concentration. These results indicate that the secretion of amino acid (N-Formylkynurenine, L-Histidine) and organic acids (isocitric acid, LL-2,6-Diaminopimelic acid, malic acid) through the metabolic pathways, including biosynthesis of amino acids, biosynthesis of cofactors, glyoxylate and dicarboxylate metabolism, and ABC transporters, is the metabolic mechanism of T. tortuosa to resist exogenous Cd stress. This study will provide a reference for the monitoring and remediation of heavy metal pollution.