The present invention belongs to the electric power technical field and relates to a method for performing impact testing by using a portable impact generator. The method can be used for testing the impact characteristics of the large-scale grounding grid of a substation. According to the method, substation grounding grid data are pre-measured at first. The method specifically includes the following steps that: soil resistivity is tested; step 2, a zero potential point is selected; step 3, a current-voltage method for remote arrangement is selected to measure the grounding resistance of the grounding grid according to the field topographical conditions and measuring conditions; and step 4, the portable impact generator is adopted as an impact excitation source to perform impact loop wiring. With the method of the invention adopted, test content which is completed by using a large impact generator can be completed. The method has the advantages of simple operation, high feasibility and high safety factor. The operating conditions of the portable impact generator just have lower requirements for electric energy, and therefore, the portable impact generator is not required to be configured with a separate diesel generator, and therefore, the portable impact generator can be small in size, light in weight and portable, and thus, test costs can be significantly reduced, test errors can be reduced, and work efficiency can be improved significantly.