Gravity energy storage system (GESS) can absorb power from the power grid or the new energy station during charging process. When insufficient charging power happens due to power fluctuation of the new energy station, two energy power flow paths of GESS can be selected to respond to charging power fluctuation, which are adjusting the number of masses or absorbing energy from grid directly. However, how to select the above paths reasonably is still a problem in engineering application. To solve the above problems, an energy flow path selection method of GESS based on benefit analysis is proposed to realize the optimal charging benefit under power fluctuation of new energy station. Firstly, taking a slope GESS as an example, two energy flow paths in the energy storage process are analyzed in detail. Secondly, with the objective of the optimal benefit, the benefit analysis model is established and power shortage threshold calculation method applied in the above energy flow paths is also proposed. Finally, in the example of a 800 kW photovoltaic power station with 250 kW slope GESS, the charging cost and benefit of energy storage system with different energy flow paths are compared and analyzed to verify the proposed method under the fluctuation of renewable energy. The results show that GESS’s charging power can be adjusted in time and power shortage of new energy power generation can also be effectively solved by using the proposed method. At the same time, power charging benefit of the system benefit can be improved by 44.95 %.