This study reports on our design of a computer system which supports the understanding of how students construct their mental representation of references and how the construction failures impede their reading comprehension. Three modules, "User interface", "Recording", and "Feedback" were implemented. The "recording module" traced all students' reading process when they tried to link sentences together by references. Results showed that more-proficient readers' mental process in resolving references was constructed to be a complete and coherent network. When they encountered reading difficulty, they usually engaged in comprehension monitoring to read and reread the related sentences to find out contextual clues. They also asked for a "feedback tool" for assistance. All these helped them grasp the main idea of a text and solve lexical ambiguities. In contrast, average and less-proficient readers often resolved the references separately or mismatched them to an incorrect subject which led to partial understanding of textual information. Their unsuccessful resolution of references in previous sentences often hindered their interpretation of subsequent sentences. This caused repeated reading failures in the comprehension of an online text. The mental maps and reading process shown in this study clearly explain students' reading success and failure. The discussion of these maps and processes between the teacher and students will be one of the ways to promote latter's awareness in employing comprehension monitoring and referring strategy. (Contains 4 tables and 20 figures.)