Software cost estimation has played an important role in software development since its emergence in 1960’s. Based on a classification of algorithmic model based methods, non- algorithmic model based methods and composite methods, the typical software cost estimation methods in history are overall reviewed. The issue of software sizing, which is closely related to software cost estimation, is also discussed in this paper. Then a three phases’ evaluation criterion of software cost estimation methods is proposed and a case study on cost estimation of government sponsored projects in China is analyzed. At last, six possible trends from estimation models, estimation evolutions, estimation applications, estimation contents, supporting tools and human factors, are presented as a primary conclusion in the paper while viewing the future development for software cost estimation.