Wet transferring two-dimension (2D) material to a semiconductor substrate is a common method to prepare a hetero-junction photodetector. When preparing to wet transfer a hetero-junction, different preparation details have significant effects on the properties of the hetero-junction formed by the 2D materials and semiconductors. In this paper, a series of identical Gr/Si hetero-junction devices were prepared by the wet transfer method and the relationship between its preparation technique and the voltage-current characteristics was studied in detail. The experimental results show that the gradient drying process can significantly reduce the dark current of the Gr/Si hetero-junction photodetector, the optimal drying temperature peak is 170 °C, and the leakage current basically no longer changes above 170 °C. The surface impurities and residual water in the inter-layer of Gr/Si van der Waals hetero-junction has a significant effect on the leakage current of the hetero-junction. The selective etching and annealing process of a Gr/Si van der Waals hetero-junction can also greatly reduce the leakage current. Therefore, a suitable drying process, selective etching process and annealing process are each necessary in the preparation of a Gr/Si hetero-junction photodetector. These results can give reference to the fabrication of two-dimensional material hetero-junction devices by the wet transfer method.