The paper aims at undetermined chara cteristics in judgment,introducin g stochastic variable in probabilit y theory,using binomial distributio n and the central limit theorem of De M oivre -Laplace that establishes a vote bounded above model and obtains the i nterval estimation of the vote resul t.In the year 2000this method is used in a college in Wuhan in evaluating professional achievements.The paper en ds with this example.