The IPSec protocol processing part in the online high speed network security processor was designed, which could process AH and ESP of network packets under both transmission mode and tunnel model. Besides, the configuration and function of the IPSec accelerator was verified with FPGA, and the ASIC verification of the IPSec accelerator which could implement AH protocol under transmission model in a single channel online network security processor with 10Gb/s date rate was also completed. The simulation results showed that the throughput data rate reached 1.5Gb/s in a single AH protocol block under transmission mode at a clock frequency of 200MHz.It could meet the network security requirements with different performances by parallel method.