This study presents a theoretical investigation of a novel Ge/Si tunneling avalanche photodiode(TAPD)with an ultra-thin barrier layer between the absorption and p+ contact layer. A high-frequency tunneling effect is introduced into the structure of the barrier layer to increase the high-frequency response when frequency is larger than 0.1 GHz, and the-3 dB bandwidth of the device increases evidently. The results demonstrate that the avalanche gain and-3 dB bandwidth of the TAPD can be influenced by the thickness and bandgap of the barrier layer.When the barrier thickness is 2 nm and the bandgap is 4.5 eV, the avalanche gain loss is negligible and the gainbandwidth product of the TAPD is 286 GHz, which is 18% higher than that of an avalanche photodiode without a barrier layer. The total noise in the TAPD was an order of magnitude smaller than that in APD without barrier layer. A high-frequency tunneling effect is introduced into the structure of the barrier layer to increase the high-frequency response when frequency is larger than 0.1 GHz, and the-3 dB bandwidth of the device increases evidently. The results demonstrate that the avalanche gain and-3 dB bandwidth of the TAPD can be influenced by the thickness and band gap of the barrier layer. When the barrier thickness is 2 nm and the band gap is 4.5 eV, the avalanche gain loss is negligible and the gain bandwidth product of the TAPD is 286 GHz, which is 18% higher than that of an avalanche photodiode without a barrier layer. The total noise in the TAPD was an order of magnitude smaller than that in APD without barrier layer.