A method and apparatus for reducing service impairment in a LAG are provided. The method includes: dividing a service packet into multiple service sub-flows, and allocating the multiple service sub-flows to all the physical ports averagely; after a new port is added, configuring a preset quantity of service sub-flows for the new port; or, after a port is deleted, allocating the service sub-flows on the deleted port to other ports; and finding a forwarding physical port through a service packet according to the service sub-flows. An apparatus for reducing service impairment in a LAG includes: an initializing module, a new port processing module or a deleted port processing module, and a forwarding port search module. In the case of adding or deleting a port, only the affected service sub-flows are operated, thus minimizing the impact.