However, unsupervised learning of sentiment is difficult, partially because of the prevalence of sentimentally ambiguous reviews<cite> (Dasgupta and Ng, 2009</cite> ). Using multi-domain sentiment corpus to sentiment classification is also hard to apply, because each domain has a very limited amount of training data, due to annotating a large corpus is difficult and time-consuming (Li and Zong, 2008) . So in this paper we focus on semi-supervised approach to sentiment classification.