An antenna assembly for microwave ablation can include a radiator for emitting a microwave for ablation； a coaxial cable for transmitting the microwave for ablation generated by a microwave generator to the radiator； an annular composite structure is provided around the coaxial cable for inhibiting an electromagnetic wave from propagating backwards along the coaxial cable. In some embodiment, the annular composite structure comprises an annular nonmetallic layer and an annular metallic layer located outside the annular nonmetallic layer. In some embodiments, the annular metallic layer is electrically insulated from the coaxial cable. In some embodiments, the antenna assembly can be used with a microwave ablation needle. The annular composite structure can inhibit the backward propagation of the microwave along the coaxial cable exterior wall. In some embodiments, circulation water enters the radiation zone, to avoid high temperatures of the head the ablation needle.
