Recently, people have paid much attention to the ultra broadband photodetectors (PDs) from the deep ultraviolet to the near infrared. However, the traditional infrared PDs made by the narrow band-gap semiconductors limited his wide application for its high cost and complex manufacturing process. The energy band engineering for two-dimensional (2D) van der Waals heterojunction with free ofsurface chemical dangling bonds is effective method for High-performance Infrared Photodetectors. In this work, we employ density functional calculation to design a type-ⅡCdTe/MoS2 heterostructure and calculate the electronic properties. The results reveal that the heterostructure has the narrow band gap of 0.64eV and electrons transfer from the CdTe layer to MoS2 layer, which promote the separation of photogenerated carriers and enhance the photoelectron conversion efficiency. The narrow band gap makes it can respond to near infrared, visible and ultraviolet light, demonstrating it the promising application for PDs. Furthermore, the analysis of molecules adsorption indicates the CdTe/MoS2 is prone to capture H2O and release the H2 molecules, which is conductive to the photocatalytic water splitting. Our work suggests that the CdTe/MoS2 heterostructure is a promising candidate as solar cell and photocatalyst, and also provides a new sight for experimental and theoretical research to design highly efficiency device.