The invention relates to a method for detecting foreign materials in an amorphous nano-crystalline alloy pig. The method comprises the following steps of: casting molten alloy into a die with the height of 20mm and the diameter of phi 10mm to form the alloy pig; removing an oxide layer on an end surface of the alloy pig by using a grinding machine, and then grinding the end surface of the alloy pig by using 200-mesh waterproof abrasive paper, 400-mesh waterproof abrasive paper, 800-mesh waterproof abrasive paper and 1,000-mesh waterproof abrasive paper in sequence; polishing the ground alloy pig by using a polisher; observing the polished alloy pig by using an inverted-type microscope to determine types of the foreign materials; and measuring the sizes of the foreign materials by using an eyepiece of a microscope with scales, and calculating the number of the foreign materials in per unit area according to the size range. By adopting the inverted-type microscope, an observing plane of a sample is horizontally arranged on the microscope, so that the angle inclination generated in the preparation process of the sample is made up; and the view field of imaging is wide, so that the accuracy of detecting the foreign materials in amorphous metal is improved. The method also has the advantages of being simple in operation, mature in process, wide in application range and the like.