We present a lumped parameter model for an adsorptive hydrogen storage system based on activated carbon. The model simply employs general mass balance and energy balance equations resulted from the fundamental conservation equations of thermodynamics. A modified Dubinin-Astakhov isotherm and a variable isosteric heat of adsorption are adopted in the lumped parameter model to improve validity for whole charge-discharge cycle. The lumped parameter model is implemented in Matlab/Simulink platform and applied to simulate charge-discharge cycle of the hydrogen storage system. Thermal averaging temperature is used to fill the gap between the multi-dimensional models, such as 0D model of Matlab/Simulink and 2D model of Comsol. The model is well validated by two sets of validation tests with the coolants of ice water and room temperature water respectively. The lumped parameter model is efficient and also accurate for predicting performance of adsorptive hydrogen storage system. Parametric studies are conducted to analyze the validity of the variable isosteric heat of adsorption, the practicality of heat transfer coefficient and the effect of hydrogen storage pressure.