The invention provides a microwave multifunctional eight-port device, which comprises four planar magic Ts and a 90-degree phase shifter, and is characterized in that two input ports of the magic T1 respectively serve as a port 1 and a port 2; two input ports of the magic T2 respectively serve as a port 3 and a port 4; two input ports of the magic T3 respectively serve as a sum output port of the magic T1 and a sum output port of the magic T2, and a sum output port and a difference output port of the magic T3 respectively serve as a port 5 and a port 6; and a difference output port of the magic T1 is connected with the 90-degree phase shifter, the other end of the 90-degree phase shifter serves as one of two input ports of the magic T4, the other input port of the magic T4 is a difference output port of the magic T2, and a sum output port and a difference output port of the magic T4 respectively serve as a port 7 and a port 8. The microwave multifunctional eight-port device provided by the invention can realize a dual-linear polarizer, a dual-circular polarizer, a six-port junction and a dual six-port junction without designing the devices independently, effectively improves reliability and maintainability of a microwave system, and satisfies microwave circuit and system modularization requirements.