The invention provides a method for measuring the wall thickness and quality defect of a steel pipe by using a rare earth permanent magnetism material. The method comprises that (1) a needed permanentmagnetism material is selected according to characteristics of the rare earth permanent magnetism material, and a device of a permanent magnetism detection unit and related auxiliary mechanism are designed; (2) the number and arrangement manner of permanent magnets are designed according to the pipe measuring thickness range; (3) magnetic field data is calculated via Ansys or related software, and a mathematical model is established; (4) a thickness application model of permanent magnets, pipe wall thickness and distance between the permanent magnets and pipe wall is established via a finiteelement analysis method or another method; (5) a pipe wall internal crack or defect detecting mathematical model is established according to detection data; and (6) a thickness value, crack depth, defect range and physical position of the pipe wall to be measured is output, and the pipe wall quality in future is predicted.