The instrument simulation of space-borne remote sensing systems is an important work for the adaptation and optimization of fundamental instrument parameters for a sensor and its observation conditions. The multispectral imaging simulator has been developed with the framework of GF-4 mission, which is a geostationary satellite in the national high-resolution earth observation system of China. The presented simulator consists of two processing modules producing GF-4 like digital number data in VNIR and MIR bands. The first processing module converts at sensor radiance to photons considering the spectral response, optical transmission, noise, modulation transfer function (MTF), et al. The second part of the simulation is electronic data processing module including an analogue-to-digital converter. The verification of the simulation is performed by comparing the real output of radiometric calibration in laboratory with simulated DN. Analysis of the final simulation data has shown the accurate and reliable performance of the established simulator enabling the system to support technical decision-making processes required for the development of the next generation geostationary satellite.