Abstract: The stainless steel pipe is easily to create the oxide-scale because of oxidation from steam. Too much exfoliation oxide-scale will choke the pipe, and even can cause the pipe-bursting. To reduce accident and cut losses, it is important to detect the oxide-scale which is formed in stainless steel pipe in boiler of power plant. Based on the technology of magnetic detection, the method to detect the oxide-scale in stainless steel pipe was presented. A set of instrument for oxide-scale testing was developed. The instrument was already widely used in the boiler of power plant. It showed that the portable instrument was convenient to test, and had high sensitivity. It could meet the demand of oxide-scale detection for stainless steel pipe in boiler of power plant.