The problems in present demonstration method of fault detection rate(R

FD

)and fault isolation rate(R

FI

)are analyzed

and the fault detection coverage percentage(R

FDC

)and fault isolation coverage percentage(R

FIC

)are taken as the testability estimation indexes instead of R

FD

and R

FI

. Therefore

a new hypergeometric distribution method is proposed for testability estimation and demonstration. Based on hypergeometric distribution

the maximum likelihood estimate method is applied in point estimation

and the Bayes formula is applied for interval estimation

hence a testability demonstration rule is provided. Simulation results show that the hypergeometric distribution method is m

ore accurate than the conventional binomial distribution method for testability estimation and demonstration under certain samples. The proposed method is suitable for the estimation and demonstration of current electronic devices.