Mold cooling system design in injection molding is critical from the viewpoint of productivity and quality of molded parts.Most of the mold cooling simulations are based on the boundary element (BEM).In this paper,a fast BEM approach for mold cooling analysis is developed.in which the mold heat transfer is considered as cyclic-steady,three dimensional conduction and formulated on the BEM.A dynamic allocation strategy is used to balance the accuracy and efficiency when generating the BEM matrix.Then the full BEM matrix is trapsformed into a sparse matrix by two methods:the direct rounding method or the combination method.This approximated sparsification can reduce the storage memory and solution time greatly.Practical examples show that the error of the direct rounding method iS too large while that of the combination method is acceptable.