Analyzed the applicability of the existing sentiment lexicon in the microblog sentiment classification. In view of low coverage of the existing sentiment lexicon, built a basic microblog sentiment lexicon by integrating the existing sentiment lexicon, and put forward a Laplacian-based smooth SO-PMI algorithm to judge emotional orientation of the words which not included in the basic sentiment lexicon, finally applied the microblog sentiment lexicon and the Laplacian smooth SO-PMI algorithm to construct the microblog sentiment lexicon, and tested the constructed lexicon classification capabilities. Experimental results showed that the constructed microblog sentiment lexicon achieved good effect inmicroblog sentiment classification.