This study compared the differences between Cantonese–Mandarin diglossia speakers and Mandarin speakers about temporal reasoning. Experiment 1 and 2 showed that whether the materials is "not to five as a unit," "5 as a unit" or "character as a unit," the reaction time of Cantonese–Mandarin diglossia speakers was longer than Mandarin speakers. The experiment 3 and 4 indicated that both Cantonese–Mandarin diglossia speakers and Mandarin speakers adopted number processing in time reasoning when the materials was "5 as a unit", but to the materials of “‘character’as a unit”, Cantonese–Mandarin diglossia speakers adopted image processing.The differences of temporal reasoning between Cantonese–Mandarin diglossia speakers and Mandarin speakers can be explained by the Weaker Links Hypothesis.