An apparatus and method for ensuring distributed packet transmission security are provided. In an embodiment of the present invention, a main control board allocates SA information to multiple processing boards according to a pre-defined criterion, so that each processing board which receives and stores the SA information may implement IPSec processing. As such, the IPSec processing is shared by the multiple processing boards. Accordingly, when there are a large number of IPSec tunnels on one interface, the IPSec processing to the packets passing the IPSec tunnels will not completely rely on only the processing board where the interface is located. Instead, the IPSec processing is allocated to different processing boards. Therefore, the multiple processing boards effectively share the IPSec processing corresponding to multiple SAs. The efficiency of the IPSec processing is increased.