Without software metrics, software would be error prone, expensive and with low quality. Cohesion is one of the most important factors for software quality as well as maintainability, reliability and reusability. The module of poor quality should be a serious obstacle to system quality. In order to design and maintain good quality software, software managers and engineers inevitably need to introduce cohesion metrics to measure and produce desirable software. In this paper, we propose a function oriented cohesion metrics is proposed.A series of experiments are shown to support the cohesion metrics,and aset of properties to evaluate the proposed cohesion metrics.Therefore,a well-defined, well-experimented and well-evaluated cohesion metrics is proposed to indicate cohesion strength and thus improve software quality.Furthermore,this cohesion metrics can be easily incorporated into software CASE tool to help software engineers to ensure software quality.