Binomial distribution IS preferred in testability demonstratlOn , but it is discrete. Because of calculation difficulty , the sampling plan IS usually worked out with some adaptatlOns. Through the research of binomial probability distribution functlOn CPDF) ,it has been proved that the PDF is a monotone mcreasmg functlon of probability p and allowable failure t1me r m test ,and IS a monotone decreasmg funCtlOn of test tlme n.With these conclusions , we present an accurate algorithm to solve the slmultaneous mequality of binomial PDF. An opt1mum solution can be worked out by adoptmg multivanate half-folded searching algorithm ,so that we can get the sampling plan of testability demonstratlOn accurately and quickly. At last we compared the calculation result with IEC1l23 ,and the correctlOn of our algorithm has been proved.