Nowadays found some micro-blog commercial extraction algorithm only considering the relationship between the key words and the number of it appearing in texts, and ignoring the key words' distribution in a certain category, which leads the decreased accuracy problems of micro-blog commercial word extraction. To solve this problem, the application of TF-IDF algorithm in words weight calculation was researched in this paper. Combining the relevant knowledge of information theory and analyzing the distribution of keywords within a class, the article proposed improving TF-IDF algorithm and applying it in term weight calculation. To test the feasibility of the improved algorithm, this paper initially classified the massive micro-blog information into certain types, and then used improved TF-IDF algorithm to calculate term weight among the categories, and, this calculation was realized under the Hadoop Distributed framework. The experiment results demonstrated that in the application of micro-blog commercial word extraction, the improved TF-IDF algorithm is effective and feasible. Compared with traditional algorithms, the improved algorithm greatly improved accuracy. In addition, the data processing speed has greatly improved under Hadoop framework.