The invention discloses an automatic machining device for improving the surface property of the internal wall of a steel pipe. The automatic machining device comprises a pipe fitting storage mechanism, a pipe fitting charging mechanism, a pipe fitting delivery mechanism and a pipe fitting sandblasting mechanism. Through two V-shaped machining stations arranged on the pipe fitting sandblasting mechanism, alternately circuiting sandblasting is carried out from ports of the left and right ends of a to-be-machined pipeline, so that the sandblasting quality is ensured and the machining efficiency is improved effectively; due to the design of the V-shaped machining stations, when pipelines having different pipe diameters are machined, the center positions of the pipelines can be kept in the same vertical plane, so that excessive adjustment on the position of a spray gun device can be avoided; and by adopting a sand collecting box, the gravel splashing and recovery problems can be solved effectively, the environmental pollution is reduced, and the safety of operating personnel is ensured. The whole automatic machining device realizes the effect of assembly line control on storage, charging, transportation, sandblasting and discharging through a PLC, is high in automaticity, and can be widely applied to rust removal treatment on pipeline internal walls of various pipeline industries.