Peer assessment has an important role in teaching and learning nowadays. However, the existing techniques tend to be limited due to a lack of a suitable means to evaluate the accuracy of peer assessment activities and supervise peer assessment performances in an online environment. Hence, it is very necessary to develop new solutions encourage students to take full effort when they join in online peer assessment activities. This study proposed a new approach to evaluate the accuracy of peer assessment results for enhancing the quality of peer assessment system. The proposed approach was applied to evaluate peer assessment activities of two groups of students. The experimental results analyzed and evaluated in terms of both the learning scores and opinion survey results, which revealed that when students realized both their own responses and their peer assessment activities were taken into account by the system in the calculation of the last score, they had positive attitudes towards peer assessment activities and the peer assessment results were improved significantly.