The mechanism on improvement of the drawability by using the fuzzy adaptive BHF (blank holder force) control has been studied in circular-cup deep-drawing process. The deep-drawing tests were carried out using aluminum alloy and cold rolled steel sheets of 1.0 mm thickness. The LDRs (limit drawing ratio) obtained from the fuzzy BHF control method and the constant BHF method in the experiment were compared and evaluated. As a result, the LDR in the case of aluminum alloy improved from 2.09 to 2.14 and in the case of the steel from 2.25 to 2.27 with the fuzzy adaptive BHF control method. The previously presented mechanism on improvement of the drawability was proved by the observation of blank deformation process. The wrinkle at the flange part under the low BHF condition was flattened due to the increasing BHF from middle to last stage of the process and then the fracture at the punch shoulder part did not happen. Moreover, from the plastic deformation model of deep-drawing operation assuming the blank material with strain hardening and anisotropic characteristics, it was confirmed that the low F value and the high γ value have a great effect on the improvement of the LDR by using the variable BHF method.