Judgement of learning (JOL) refers judgment made by participants at the end of a learning trial regarding the likelihood of remembering the acquired information on a subsequent memory test. JOL is an important form of metacognitive monitoring,as it affects metacognitive control,for example,learning time distribution and choice of restudy directly or indirectly. The UWP(underconfidence-with-practice ) effect has been the study hotspot of JOL. although many theories try to explan the cause of UWP effect, none can perfectly give the answer. According these theories, great attentions are paid to the external factors such as learning materials and learning methods,few studies concern individual differences among studies. This research tries to prove whether emotion is one of the factors that lead to UWP effect, if so,the current study also tries to explor the mechanism and individual differences. Two experiments are conducted. Experiment 1 explors whether emotion affect JOL, experiment 2 focus on the internal mechanism, the results show are as follows: (1) The first trial of memory test can affect JOL,recall and absolute accuracy of JOL by individual’s emotion. (2)Emotion can affect JOL and individual’s depth of cognitive process for study, which will promote individual’s memory. JOL and recall together influence the accuracy of JOL.