This study mainly investigated into the influential factors of enhancing English vocabulary learning ability of elementary school students, gathering and referring to relevant literature and the application of modified Delphi method (MDM). Four factors which are teaching theory, teaching style, teaching material and learning motivation, respectively were obtained in this study. A hierarchical structure was established, and then the Analytic Hierarchy Process (AHP) was applied to finding the relative index factors of the four aspects and to build up the weights for the hierarchy model. Based on the four main criteria in this study, the results show that the most significant indicator is "learning motivation", followed by "teaching style", "teaching material", and at last "teaching theory". In terms of fifteen sub criteria, learning participation, learning center and learning task are more important than other factors. This also reflects that students are the primary consideration in learning, and the teaching process is to assist students to obtain learning ability.