This study investigated the mapping directionality of Mandarin synaesthesia, based on a self-paced reading task. We have found that Mandarin synaesthesia also shows mapping directionalities in the language comprehension among native Mandarin Chinese speakers. However, the results of the self-paced reading task do not support the direction of Mandarin synaesthetic mapping from vision to smell found in previous corpus studies. As the reading task makes up for the limited quantity of olfactory words in human languages, synaesthetic mapping directions attested in this study would be the most likely to reflect the actual pattern of Mandarin synaesthesia. In addition, the self-paced reading task demonstrates different characteristics among the linguistic expressions without synaesthetic usages, the expressions following synaesthetic mapping directions, and the expressions incongruent with synaesthetic mapping directions in the reading process. These patterns provide evidence for linguistic synaesthesia as an independent cognitive mechanism, which furthers our understanding of linguistic synaesthesia and metaphor.