The invention relates to a method for in-situ detection of a blade boss defect. The method comprises the following steps: S1. clamping a probe to which an eddy current sensor is clamped to a to-be-detected area of a blade boss, then energizing the eddy current sensor to generate induced current in the blade, collecting an induction signal of the eddy current sensor, and observing a display screenconnected with the eddy current sensor; S2, performing zero setting on the collected induction signal; S3, amplifying the induction signal subjected to the zero setting by using processing software; S4, setting a threshold line, comparing the amplified induction signal with the threshold line, and using a color line segment different from the threshold line to indicate a comparison result; and S5,repeating the above steps, and judging whether there is a defect based on the comparison result and the threshold line step by step. The method provided by the invention has the effects of enabling aworker to intuitively understand whether the blade has the defect and improving the detection accuracy.