Abstract: The boundary element method (BEM) in injection molding cooling analysis generate full-matrix equations. If the element number is too large, its calculating work will be beyond the computer’s ability. There is no valid numerical method to solve these equations today. The key problem is the computation speed.This not only means a long time of computation, but also means that the calculation does not convergent easily.This paper presents a new method to deal with the problem. Because the temperature variation on mold surface is successional, when two points are close to each other, their temperature is nearly equal. So the new method neglected the temperature difference and incorporated the adjacent elements in one group. After incorporation, the size of cooling model was reduced. The average temperatures of elements in one group were solved firstly. Using these temperature results, the temperature of every element in one group would be computed in the next step. In this way, one large size equations was decomposed into several small size equations. The computational work was reduced and the calculating time was less than one quarter of the conventional method.On the other hand, element incorporation reduced the size of data and helped to weaken the effect of truncation error which caused distorted results. This could enhance the treatable number of element one time more than that of original method.