In the study, one web annotation system VPen was proposed for facilitating students to foster metacognition by reviewing self and others' annotation and homework. Annotations are personally meaningful and useful for individual reflection later, while homework sharing is generally useful for all because it is assigned by instructors. Therefore, through reviewing these two products, annotation and homework, some metacognition may occur. We conducted the quasi experiment employing VPen system to study the influence of reviewing annotation and homework on Math learning. The results showed that reviewing self's annotation and homework had significant influence on learning achievements. Regarding consulting others' annotation and homework, some interesting different phenomena were obtained; for consulting others' annotation, less usefulness was found on learning achievement because annotation is usually meaningful and useful to it owner only, while consulting others' homework is more useful because all students need to solve homework and can get much benefits from studying other solving methods. From this study, we suggested that the design of learning activities should consider not only taking annotation and homework but also promoting students to review them in order to foster metacognition.