The purpose of the present study was to identify the potential components influencing second language (L2) vocabulary acquisition and their structural process to L2 vocabulary knowledge. For the current study, 129 4th-grade students in an EFL context were invited, and they were assessed in productive/receptive vocabulary tasks and responded to questionnaire survey on L2 vocabulary acquisition strategies. The vocabulary test consisted of synonyms, antonyms, and analogies adopted from Woodcock-Johnson Ⅲ Diagnostic Reading Battery (Woodcock, Mather, and Schrank 2004) and the questionnaire was composed of 24 items concerning L2 vocabulary learning strategies. According to factor analysis, four factors of L2 vocabulary acquisition were found: vocabulary learning strategy, extra-curricular activities, parents` interest on their children`s English learning, and first language (L1) proficiency. Regression analysis unveiled that L2 vocabulary learning strategy and extra-curricular activities were significant indicators of L2 vocabulary knowledge. In addition, based on structural equation modeling (SEM), L2 vocabulary learning strategy made a significant direct effect on L2 vocabulary performance. These findings suggest that L2 vocabulary learning strategy plays a critical role in progressing L2 vocabulary achievement, as proposed in Involvement Load Hypothesis (ILH: Laufer and Hulstijn 2001) as well as extra-curricular activities positively impact on L2 vocabulary improvement. Moreover not only L1 vocabulary knowledge but also parents` interest in their children`s English learning cannot be excluded for successful L2 vocabulary acquisition.