This study aims to assess the effect of calibration relevant to metamemory in English vocabulary learning. The participants of this study consisted of 110 ninth-grade junior high school students from New Taipei City and were divided into high-proficient and low-proficient groups based on their initial test score. Before each English vocabulary test, the students were asked to predict their vocabulary test score. Time series analysis was applied to explore the effects of the students' calibration in English vocabulary learning. The results showed that using the calibration technique with metamemory is more useful for the students in the low-proficient group than those in the high-proficient group and can enhance the learning of low-proficient students to effectively memorize English vocabulary.