The invention provides a method for implementing varying service quality grades in a network switch. First, a plurality of users of the network switch is classified into a plurality of service quality grades according to a contributing factor of the plurality of the users. Each of the plurality of users is then connected to the network switch via one of a plurality of ports of the network switch according to its service quality grade. An original priority of a packet in the network switch is then determined. An adjusted priority of the packet is then determined according to both the original priority of the packet and a priority adjustment table of an ingress port of the packet. Each of the plurality of ports has a corresponding priority adjustment table, and each of the priority adjustment tables includes a mapping relationship between the original priority and the adjusted priority.