Abstract: The macroscopic and microscopic features of abnormal and normal areas were compared and analyzed in view of the "white spot" defect of low-pressure turbine disc forgings of an aeroengine. The results show that the abnormal area is the "white spot" produced by visible lean Nb segregation, and its macroscopic size exceeds 8 mm technical requirements. The grain size of abnormal region is 2 grade, which exceeds the technical requirement of 10 grade. There is a mass of inclusions near the "white spot", the inclusions are oxide inclusions of Mg and Al. According to the analysis results combined with the ultrasonic C-scanning map of the forging, the monitoring measures from raw materials, disc billet and forgings were put forward.