Abstract: To improve the sentiment classification precision,the paper proposed a method to determine the certainty of sentiment.The method takes account of multiple sentiment features of vocabularies in the sentiment database and identifies the clause giving opinions.It classifies the clauses into different emotinoal polarities through machine learning.The experiment shows that the proposed method employing the certainty of the sentiment unifies the emotional polarities measurement.It has a better performance on identifying the clause giving options and emotional polarity classification.

Key words: Emotional polarity certainty,Sentiment classification,Sentiment sentence recognition,Emotional polarity classification,Microblog