This paper demonstrates a Verilog-A compact photonic model based on coupled-mode theory for nonlinear interactions, including four-wave mixing (FWM) and cross-phase modulation (XPM), to present a general framework and methodology for modeling nonlinear interactions in electronic-photonic co-simulation. The model is compatible with existing electronic design automation (EDA) platforms and can support rapid electronic-photonic co-simulation. It avoids describing the complicated physical process of the FWM and provides an easy way for system designers to monitor the dynamics of the critical optical parameters, thus accelerating the co-design and co-optimization of the electronic-photonic hybrid systems incorporating FWM. Meanwhile, the model is not tailored for a particular photonic device but can be applied to different photonic devices as a fundamental component. The model framework and modeling methodology presented in this paper are expected to be further applied to the modeling of other optical nonlinear interactions. The simulation results of the proposed model agree well with both numerical and experimental results. A closed-loop electronic-photonic co-simulation example using the proposed model is also carried out successfully.