For light-emitting diode (LED) package, interface delamination is a key factor that triggers reliability issues. When the delamination occurs in the thermal path of the die attach (DA) layer, the heat transfer capacity will be blocked and the junction temperature of the device will increase, which will affect various other failure mechanisms and ultimately reduces the life of the LED package. In this paper, the finite element method is used and based on entropy generation analysis. Interfacial delamination is prefabricated to the upper and lower interfaces of a model. The effects of cracks simultaneously appearing at different positions and lengths of the upper and lower interfaces on heat transfer are compared. Based on the simultaneous results, in the same position of the DA layer, the entropy generation value of delamination is larger than that without delamination, and the entropy generation value of delamination in the same position of the upper and lower interfaces is greater than that of not located in the same position. The larger the entropy generation value, the worse the heat transfer performance. And cracks appearing at the edge of the upper and lower interfaces have greater damage on heat conduction than the middle position. In addition, as the delamination length simultaneously increases at the upper and lower interfaces, the heat transfer performance becomes worse.