Through a semantic processing task priming paradigm, this research investigates the priming effects of the matching task of macro-categories on micro-category in metaphor processing, hence taking an insight into the realization mechanism of metaphorical categorization. The result shows that in the semantic structure mapping task, even without being explicitly demanded to recognize the category relation between the topic and the vehicle, the shortened reaction time to category associated target demonstrated that the mapping task activated the category association between the topic and the vehicle, yet the same priming effect was not found in pure semantic associating task. In contrast to pure semantic associating task, the priming effect of the mapping task exerted on category target indicates that the categorization of the topic and the vehicle is based on the structural mapping between the semantic relations involving the topic and the vehicle and the corresponding objects. This study provides further empirical evidence for the first-matching-later-projecting model in metaphorical categorization.