Abstract:The trees were selected in three aspects: Qualitative characters, quantitative characters and resistance. But we paid much attention to quantitative characters evaluated by standard selection differential. The quantitative characters and resistance were assessed with independent criteria.Four most important factors have been found out by means of double selection stepwise regression from eighteen variables which include the characters of plus trees and the sampling statistics. Eleven characters of plus trees were divided into five groups and the plus trees were separated into four parts by principal component analysis(PCA).According to the results obtained from these analysis, it was shown that quantitative characters were more accurate and to be used easily by standard selection differential of the tree heights. And four criteria have been proposed to estimate plus trees.