There has been a growing trend of the study on prospective memory in human’s daily life in recent years. The present study is about how prospective memory failure in daily life situations is attributed and what factors affect the attribution. Based on the 6 attributions (poor memory, carelessness, reluctant, temporary emergency, no attention and force majeure) to prospective memory failure in daily life which were concluded from an open question, we developed a 12-scenario questionnaire to confirm the influence of the events' importance (importance, unimportance), relationship (parent-child relationship, friendship, stranger relationship) and failure (self, others), so the influence of the events' importance, relationship and prospective memory failure were investigated in a 2 × 3 × 2 design to explore how attributions to prospective memory failure were affected by these three factors. 124 college students were asked to attribute prospective memory failures in the 12 scenarios. It was found that (1)the most prospective memory failures were attributed to carelessness, and the fewest were attributed to reluctant; (2)the former 6 attributions can be summarized in three factors(unintentional, deliberate and objective) according to the results of EFA; (3)all the three factors--importance, relationship and failure affected the attribution of prospective memory failure: subjects more likely attributed blame to the unintentional in unimportant events, and to the deliberate in important events. When evaluating the seriousness of the events and the moral character of those who forgot things, the subjects tended to be stricter on their own and more tolerant to others, light duty and slight consequences in parent-child relationship were found as well as heavy responsibility and serious consequences in friendship when facing important events. In addition, more researches such as cross-cultural studies can be done in future to further clarify the attributions to prospective memory failure.