Security analysis is an indispensable part of practical quantum key distribution (QKD) protocol, which can not only evaluate the eavesdropping ability of external attacks, but also provide a security bound for the key rate of system. Quantum channel attack is the main content of QKD security analysis, among which collective attack is considered to be one of the most powerful quantum channel attacks. In this paper, a generalized collective attack operation, composed of generalized bipartite coupling and the optimal positive operator-valued measurement (POVM) is constructed, and a theoretical study on the security analysis of E91-QKD against collective attack is carried out. The simulation results show that under collective attack, the mutual information between the eavesdropper and the communicator is less than that proposed by the entanglement purification protocol, and the key rate and bit error rate tolerance have been significantly improved. The security analysis developed in this work provides a theoretical method to increase the key rate for practical QKDs, which can be compatible with other experimental methods.