Abstract: A large number of full-scale model tests and field monitoring results show that soil nail internal forces have excavation effect. The maximum tension of soil nail appears in the middle of the foundation pit, the upper and lower internal forces are smaller. But the design and calculation theory of norms "Technical specification for retaining and protection of building foundation excavation" (JGJ 120——99) and "Specification for soil nailing in foundation excavation" all cannot accurately reflect the actual soil nail internal force we prototype observed at the scene. The above issues bring difficulty to reasonably determine the length of soil nail, make the calculation of internal forces and the length of soil nail rely more on experience, and lead to the design of soil nail forces unsafe or conservative. Here we analyzed the soil nail force calculated by current regulations is not consistent with the measured soil nail force, pointed out the defects existing in the current regulations calculation method, analyzed the effect of earthwork excavation of soil nail force, and discussed a simplified soil nail internal force calculation method based on incremental method.