Abstract: The packet loss differentiating mechanism of TCP for heterogeneous networks plays an important role in the stability of wireless networks, relative one-way delay (ROD) of packet pair is used as the differentiating parameter to distinguish the loss type. The accuracy of this algorithm depends on ROD samples membership functions and parameters estimation. In order to differentiate the packet loss pattern more accurately, the initialization method based on potential functions is proposed by analyzing the traditional expectation maximization (EM) algorithm in Gaussian mixture model. Then the improved EM (PEM) algorithm is applied in the construction of different packet loss membership functions in the situation when the network congestion and wireless error coexist. The simulation results indicate that this algorithm has better convergence characteristics and stability, and has well building effect in the construction of different packet loss pattern membership functions.