Once graphene was discovered, it has attracted the attention of the scientific community because of its excellent mechanical, electrical and optical properties, and has pushed the development of nanotechnology to an unprecedented height. Two-dimensional (2D) Transition Metal Chalcogenides (TMDs), as an important part of nanomaterials, not only inherit the excellent physical properties of Graphene, but also make up for the shortcomings of photoelectric applications caused by the zero-band gap and semimetal properties of Graphene. It is found that transition metal chalcogenides have widespread application value in photoelectric devices, spintronics, catalysis, biochemical detection, supercapacitors, solar cells, lithium ion batteries and other fields. It is worth noting that two-dimensional Janus structural materials, as a new type of two-dimensional layered nanomaterials, have more abundant photophysical properties than traditional transition metal chalcogenides on account of the different types of atoms on both sides of the transition metal in the Janus structure, and their various surface interface structures that provide convenient conditions for the construction of different types of heterojunctions. Therefore, the calculation and analysis of the photoelectric properties of two-dimensional Janus structural materials and related heterojunctions has been an important aspect of theoretical research on two-dimensional layered nanomaterials in recent years. At present, there are relatively few reports about the dielectric properties of two-dimensional Janus materials, and the analysis of the generation mechanism of dielectric properties needs to be further strengthened.The traditional density functional theory has become an indispensable calculation method for the theoretical study of the physical properties of multiparticle systems. Due to the existence of van der Waals interaction in 2D layered nanomaterials and the tremendous influence of electron orbital hybridization on their photoelectric properties, we use density functional theory, van der Waals correction and hybrid functional to calculate and analyze the multi-particle system to obtain a result close to the experiment.First, the electronic properties and optical dielectric functions of Janus structural materials MXY (M=Zr, Hf; X/Y = S, Se) and its related heterojunctions are calculated and analyzed. It can be found that the results of the band gap values of the IVB-VIA Janus structure material are in good agreement with the experimental values after correction by first principles with hybrid functionals HSE06. The electronic structures indicate that the monolayer ZrSSe and HfSSe are indirect bandgap semiconductors with band gaps of 1.196 0 eV and 1.040 2 eV, respectively. The remarkable band nesting that appears on band structure means light-matter interaction strongly. By comparing the state densities of the materials, it can be found that the positions of the Conduction Band Minimum (CBM) and the Valence Band Maximum (VBM) of the two structures are mainly related to the transition metal atoms and chalcogens atoms, respectively. The correlation analysis of dielectric properties and band structure shows that the appearance of the peak is mainly related to the electron transition occurring between the first, second and third valence bands and the first, second and third conduction band after the absorption of photons. In addition, due to the p orbital electron transition of S and Se atoms, the material exhibits excellent photon absorption properties in the infrared and visible regions. The local planar-averaged DOS proves the existence of three kinds of heterojunctions based on ZrSSe and HfSSe with different interface characteristics and the charge density associated with the band edge is distributed over both materials. Notably, the absorption peaks of ZrSSe/HfSSe heterojunctions are in the infrared and visible range, up to 1.26×10⁶ cm^-1. At the same time, the calculation of the energy loss spectrum also shows that ZrSSe/HfSSe heterojunctions has a high absorptivity in the range of visible light. This work not only effectively reveals the photophysical properties of Janus structural materials and their heterojunctions, but also promotes the potential applications of these materials in new types of optoelectronic devices.