The invention discloses a lifting force detecting method for the accumulating amount of oxide scale in an austenitic stainless steel elbow pipe of a boiler, which comprises the following steps of: (1) selecting a sample pipe; (2) adding oxide scale into the sample pipe; (3) carrying out magnetization processing on the oxide scale accumulated in the elbow pipe; and measuring a magnetic field lifting force value of the oxide scale in an elbow of the sample pipe; (4) and (5) making a relation curve figure between the accumulating amount of the oxide scale in different sample pipes and the corresponding magnetic field lifting force values; (6) carrying out magnetization processing on the oxide scale accumulated in the elbow pipe in the detected boiler elbow pipe and measuring the magnetic field lifting force value F of the oxide scale accumulated in the elbow pipe; and (7) searching out the accumulating amount of the oxide scale in the detected boiler elbow pipe by using the relation curve figure. The method can carry out nondestructive detection on the oxide scale in the austenitic stainless steel elbow pipe of the in-service boiler without special processing and has the characteristics of simplicity, safety, reliability and high sensitivity.