Study shows that the displacement distribution of brittle fault population exhibits self-similarity and has the power-law relationship between displacement and accumulation. In other words, brittle fault population follows the fractal size distribution. The extensional quantity of a basin can be estimated based on this result (fractal method), which demonstrates the contribution of cumulative extension of a small fault to the whole one, and accounts for the discrepancy between the plain spastic restoration and the other methods. Taking the Bohai basin as an example, the principle and procedures of this method are introduced in detail and good fits have been obtained in the study area.