The invention relates to a measuring method in sheet metal component machining, in particular to a sheet metal flanging loss measuring method. The sheet metal flanging loss measuring method comprises the steps of: 1, forming at least three circular holes in an outer plate ; 2, placing corresponding semicircular adapters in the circular holes; 3, scanning the outer plate via a computer; 4, forming a vertical cross-section at a flanging place to form a first cross-section line and a first measuring end point; 5, subjecting the outer plate and an inner plate to flanging snap-in; 6, scanning an assembly; 7, forming a vertical cross-section at a flanging place of the assembly to form a second cross-section line and a second measuring end point successively; 8, and fitting the first cross-section line and the second cross-section line corresponding to the assembly before and after the flanging of the outer plate, measuring the distance a from a measuring starting point to the first measuring end point and the distance b from the measuring starting point to the second measuring end point, calculating a difference value between a and b to obtain a flanging loss value FV. The sheet metal flanging loss measuring method can be used for analyzing flanging loss at any position, can store the flanging loss for comparative analysis at any time, and is conducive to tracing data and mastering flanging loss law.