According to modular theory, there are interactive effects between the central modules and language modules. The central cognition may deploy and redeploy resources from language modules. Moreover, the language modules can activate the cognitive ability. So this paper studies the spontaneous speech of students who learn English as a foreign language, to check whether activated syntactic module could speed up speech processing or not, and whether activated semantic module could also influence selection of syntactic structures. Therefore, this paper mainly conducts a qualitative study on English subjunctive mood based on the analysis on related syntactic and and semantic factors in Chinese learners' spontaneous speeches, aiming at exploring the influence of syntactic and semantic modules on subjunctive mood learning. The result shows there are interactions between syntactic module and semantic module: the activation of either module will speed up speech processing of the other. Therefore in the teaching of Chinese learners' English spontaneous speech, the teachers should take measures to strengthen the input of the language modules in an applicable atmosphere, so that the two modules can reinforce each other, thus improving students' spontaneous speech ability effectively.