In Mandarin the space-time word “前/qian” is used to express both the spatial concept of front/forward and the temporal concept of early/before. In Chinese Sign Languages, however, the spatial front/forward and the temporal early/before are signed differently as the sign for spatial front is only used for the spatial concept of forward, and the sign for before/past is directed to the back. In this study we investigate whether the Mandarin sagittal space-time metaphors influence Chinese deaf signers’ spatio-temporal reasoning. In two experiments, we found that signers with higher Mandarin proficiency were more likely to interpret the Mandarin word “前/qian” as the temporal past (Study1), and to perform past-in-front space-time mappings (Study2) as opposed to signers with lower Mandarin proficiency. The findings not only provide within-culture evidence for the influence of language on thought, but also demonstrate that even cross-modal space-time metaphors can impact deaf-signers’ spatio-temporal reasoning.