Aiming at the problem that the impact force calculation model cannot accurately link the contact force with local deformation, theoretical calculation and experimental research were conducted on block impact to improve the calculation accuracy of the rockfall impact force and impact energy, and then optimize the design of the protective net. Firstly, the elastic net was considered as an elastic film, and the Dirac function was introduced to divide the "unidirectional uniform tensile zone" and the "bidirectional uniform tensile zone". Secondly, the calculation formulas for the impact force and energy of falling rocks were derived through the Galerkin method, and impact tests were conducted on the elastic nets with different pretension force. Finally, the deformation of the elastic mesh was substituted into the above formula to calculate the impact force and impact energy, and the reasons for the errors were analyzed. Correction coefficient was proposed to correct the results. The maximum errors of the corrected impact force and energy are 2.8% and 3.9%. Compared with the existing methods for calculating the impact force and impact energy of rockfall, the proposed calculation method is more simplified. It can be used to calculate the impact force and energy of falling rocks in model experiments, providing a basic basis for optimizing the design of falling rock protection.