Abstract: Analysis of the many current middle school mathematics textbooks in use finds that the understanding models concerning the concept of “two negatives make a positive” fall into four categories: the analog model; the inductive model; the deductive model and the situational expository model. From the learners' perspective, an efficiency analysis is made into the four models in the process of helping students understand the concept of “two negatives make a positive”, thus to put forward a new understanding model for the comprehension of the concept.