Prospective memory refers to the ability to remember to carry out the planned event or activity in a given time or situation in the future. According to the nature of the clue, prospective memory is generally divided into event-based prospective memory and time-based prospective memory. We focus on time-based prospective memory. The time-based prospective memory needs to be executed at a specific time period or a specific time point. Prospective memory is easily influenced by external factors, such as negative emotion. Negative emotion is an unpleasant state, which usually disintegrates our cognitive processing. A large number of studies have found that negative emotion interferes with prospective memory performance. Some evidence shows that interference of negative emotion to prospective memory may be influenced by cognitive resources. However, some studies argued that delay could provide participants more cognitive resource for processing prospective memory tasks. Our aim was to explore that whether the interference of negative emotion to prospective memory can be eliminated through adding the delay . We directly explored two problems: (1) whether negative emotion had an impact on prospective memory; (2) whether the delay could eliminate the interference effect. Emotional pictures were selected from Chinese Affective Picture System (CAPS). The procedure was written in E-Prime 1.0. Ongoing task was n-back (n=1) tasks. we adopted multiple indicators as a basis for judgment. Firstly, the comparison of the results of prospective memory indicated that whether negative emotion interfered with prospective memory. Secondly, comparing the difference of time monitoring, to a certain extent, reflected the cognitive processing degree of prospective memory tasks. In addition, the number of attention in the later period of time monitoring reflected the effectiveness of time monitoring. The results of experiment were as follows: (1) The score of prospective memory in negative emotional group was worse than that in neutral emotional group when there was no delay, but in the delay condition, there was no difference between the negative emotional group and neutral emotional group. (2) The number of time monitoring in total in negative emotion group was less than that of neutral group. (3) The number of time monitoring in the later period of negative emotion group was worse than that of neutral emotional group when there was no delay, but in the delay condition, there was no difference between neutral emotional group and negative emotion group in the same index.（4）The reaction speed of negative emotion group was slower than that of neutral emotion group in ongoing task. The above analysis shows that negative emotion can interfere with time-based prospective memory, but delay can eliminate the interference effect. The interference of negative emotion on prospective memory is mainly influenced by the attention input and effectiveness of monitoring. The elimination of interference effect through adding the delay is mainly due to the improvement of monitoring effectiveness. However, delay does not eliminate the interference of negative emotions on ongoing task. In conclusion, negative emotion interferes with prospective memory, the setting of delay can eliminate the interference effect through improving the effectiveness of time monitoring.