To enhance the learners' performance and learning efficiency on e-learning platform is an essential issue in current teaching and learning engagement. This paper applies IT techniques and analysis methods to visualize the learners' user relationship on the discussion board of Moodle based on the replying order and times they made in the selected topics/forum in a Moodle course, which will be very useful in the future for embedding the visualization into large-scale systems and further development of related applications. We mainly first extract the inner relation of users' participation in one/several selected discussion topics or a whole forum of a certain course. Then we visualize the user participation relation using Scalable Vector Graphics (SVG) provided by D3.js with aesthetic graph visualization. Our visualization with directed graph (digraph) structures provides easy understanding of users' network connections in topics/forum, and the weights of the connections indicating the replying times are shown both numerically on edges and visually by the thickness of edges. Digraph is applied here to indicate different replying order. We propose to perform visualization construction and representation via PHP with latest advanced programming libraries of jQuery and D3.js, while easy control of tree-structured menu for user relation visualization is realized by jsTree. In the experiments, our method consistently demonstrates high-quality detailed visualization of users' underlying relation structure they belong to, which may benefit the further study of improving the learning efficiency on e-learning platform.