With the transformation of global energy, the development of hybrid energy system of nuclear energy and other clean energy is a new research direction. As a representative of the generation IV nuclear energy system, modular high temperature gas-cooled reactor (MHTGR) can provide high quality steam for multiple usage. In this paper, the copper-chlorine (Cu-Cl) cycle and high-temperature electrolysis (HTE) hydrogen production are proposed as the backup processes of the multiple MHTGR unit, and the dynamic model of the cogeneration plant is established according to the conservation of mass, energy and momentum. Furthermore, the coordinated control system of cogeneration plant is proposed to realize load following control. It is programmed on MATLAB/Simulink platform and verified by numerical simulation, and the results show that the model and control scheme of cogeneration plant proposed in this paper is feasible to realize the load following function of stable grid frequency.