Graphene has good electrical and optoelectronic properties, and the heterojunction photodetector formed by the combination of graphene and silicon semiconductor materials has excellent photodetection properties. The band gap of silicon is 1.12 eV, resulting in the cut-off wavelength of silicon-based near infrared ray photodetectors generally around 1.1 µm, and its detection wavelength range is relatively narrow, and Ge-based photodetectors can detect longer-wavelength near infrared ray light.In this study, a graphene/germanium Schottky junction photodetector in the near-infrared communication band was fabricated. First, high-quality graphene was prepared on the surface of copper foil by chemical vapor deposition method. Subsequently, the graphene was transferred to n-Ge surface by the wet transfer method, thus forming a Schottky contact. Finally, a high-performance graphene/germanium Schottky junction device is obtained by depositing gold electrode on the front side of the germanium substrate and spin-coating the In-Ga electrode on the back side.By simulating the photon absorption rate in the two-dimensional structure of the n-Ge substrate with Synopsys Sentaurus TCAD, the unique distribution of the photon absorption rate can be seen. When the wavelength of the incident light is short, the penetration depth of the incident light is very shallow (less than 10 nm), indicating that photons are almost absorbed in the surface of the heterojunction. Due to the existence of surface defects and/or dangling bonds, there is severe carrier recombination in this region, which reduces the photoresponse. But as the wavelength of the incident light increases, the penetration depth will gradually increase, reaching the strongest absorption at 1 600 nm. With the introduction of the graphene transparent electrode, it will form a good Schottky contact with the germanium substrate, which greatly improves the photo-generated carrier collection efficiency of the device. As the incident wavelength increases from 265 nm to 1 550 nm, the generation of electron-hole pairs will gradually expand from the depletion region of the monolayer graphene/n-Ge junction to the diffusion region, causing the photodetector has different responses with different wavelengths. Using the band diagram of the junction and the carrier transport process to analyze and explain the working mechanism of the detector, the Fermi level (E_F) of graphene is 4.7 eV. The resistivity of n-Ge is 1~10 Ωcm^-1, and its work function is about 4.37 eV. After the two materials form a Schottky junction, electrons diffuse from germanium to graphene due to the difference in work function, while holes are formed in the depletion region of germanium. This charge transfer breaks the original respective energy band balance, the energy levels near the germanium surface bend upward, and a built-in electric field appears. The depletion region of germanium produces electron-hole pairs when exposed to light with energies exceeding the forbidden band width of germanium (0.67 eV). Carriers generated near the depletion region diffuse into the depletion region. Subsequently, the electrons and holes are rapidly separated by the built-in electric field, the electrons are collected at the bottom In-Ga electrode, while the holes are transferred through the graphene and finally collected by the gold electrode at the upper surface.The same is true of the experimental results, the graphene/germanium Schottky junction shows obvious rectification characteristics, and the rectification ratio of the device is about 5.3×10² under the condition of ±1 V without illumination, which is better than many previous Ge-based heterogeneities structure. The detector shows good switching characteristics and good repeatability for pulsed light at different frequencies (1 kHz, 5 kHz, 10 kHz), indicating that the device has good operability over a wide modulation frequency range. After 5 months in the air environment, the photocurrent almost did not decay, and it still maintained its excellent optical switching characteristics, showing good stability. The device also exhibits obvious photoelectric response performance. Under the irradiation of 1 550 nm near-infrared light with a light intensity of 0.3 mW/cm², the responsivity and detection rate of the device can reach 635.7 mA/W and 9.8×10¹⁰ Jones, respectively. At the same time, the device has a fast response speed, with rise and fall times of 40 μs and 35 μs, respectively, at a 3 dB bandwidth. The potential applications of high-performance graphene/germanium photodetectors in near-infrared optoelectronic systems are demonstrated.