Organic donor–acceptor systems have attracted much attention due to their various potential applications. However, the rational construction and modulation of highly ordered donor–acceptor systems could be a challenge due to the complicated self‐assembly process of donor and acceptor species. Considering the well‐defined arrangement of species at the molecule level, a crystalline host–guest system could be an ideal platform for the rational construction of donor–acceptor systems. Herein, it is shown how the rational construction of highly tunable donor–acceptor materials can be achieved based on a crystalline host–guest platform. Within the well‐established metal–organic framework NKU‐111 as the crystalline host enabled by the relatively stable coordination‐directed assembly, the introduction and arrangement of guest molecules in the crystals allow the rational construction of the NKU‐111⊃guest donor–acceptor system. The donor–acceptor interaction in the systems can be readily modulated with different guest molecules, which can be justified by the well‐demonstrated guest‐dependent characteristics. Accordingly, the NKU‐111⊃guest reveals highly tunable donor–acceptor properties such as charge‐transfer‐based emissions and electrical conductivity. This work indicates the potential of crystalline host–guest systems as an ideal platform for systematic investigations of donor–acceptor materials. A donor–acceptor material based on a host–guest crystalline material platform is raised. As a proof of concept, a metal–organic framework (NKU‐111) is utilized as a host acceptor for the accommodation of aromatic donor guests. The resulting donor–acceptor system features highly tunable charge‐transfer‐based emissions and conductivity, indicating the rationality and efficiency of this strategy.