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