The invention relates to an outer-pipe circular cutting robot for a steel pipe. The robot comprises a base, a steel pipe pressing plate, a circular cutting frame, an expansion link sleeve, an expansion link, an expansion link motor, a cutting mechanism fixing plate, a rotary motor, a cutting blade, an electric brush, an expansion link rack and an expansion link cutting motor fixing frame, wherein steel pipe frame stand columns of the expansion link motor fixing plate is fixedly arranged on the base, a steel pipe fixing sleeve is fixedly arranged on the steel pipe frame stand columns, the circular cutting frame is fixedly arranged on circular cutting frame stand columns, and the circular cutting frame stand columns are fixedly arranged on the base; the expansion link is arranged on the expansion link sleeve in a sliding way, the expansion link motor is fixedly arranged on the expansion link motor fixing plate, a stretching motor gear is fixedly arranged on an expansion link motor shaft, and the stretching motor gear is meshed with the expansion link rack; and the cutting motor is fixedly arranged on the expansion link cutting motor fixing frame, and the cutting blade is fixedly arranged on the cutting motor shaft. The robot can improve the steel pipe cutting efficiency, and is high in cutting speed, trim in notches and good in effect.