Software cost estimation has been an important part of the software project management. Afterover half a century of research and industrial practice, cost estimation methods and models have been greatly enriched. A variety of cost estimation tools are derived from these methods and models. However, cost estimation methods and models are based on historical project data. Companies and organizations without historical project data can only use data from other companies or organizations to do the cost estimates of their own projects. How to effectively do cost estimationwith cross-company data becomes more realistic. Aiming at this problem, we propose a new cost estimation method to use cross-company data effectively. The experiments show that the method could improve the accuracy.