The invention discloses a method for detecting internal corrosion of a steel pipeline, which belongs to the field of nondestructive measurement. The method includes that a coil center is placed above the pipeline and approximately parallel to the pipeline; an inducting coil is in reversed-phase series connection with a compensating coil; when a current is switched on, magnetic fields generated atthe positions of magnetometers at the centers of the inducting coil and the compensating coil have equal intensity and opposite directions. As the inducting coil is large and has more circles, the magnetic fields are strong in intensity and deep in penetration depth, and a magnetizing field is generated on the pipeline, thereby corrosion degree and space distribution of corrosion portions of the steel pipeline can be confirmed according to degree and distribution of magnetic anomaly of artificial magnetization. The method has the advantages of no need to stop production, dig and work inside the pipeline, nondestructive detection, simple equipment, convenient power supply and small power consumption.