Software metrics is one of the most active research areas of software engineering. In this paper, a process model for software process metrics is proposed, which defines the roles, activities and related supporting tools and methods for the implementation of software process metrics, and gives an emphasis on the description of the goals, tasks and methods for the activity of process data collection, validation and analysis. Architecture of a process metrics infrastructure supporting software process Metrics is presented. Furthermore, an application of this model in a large-scale software enterprise is given to demonstrate its effects on software process assessment and improvement. The research result is greatly helpful and can be widely used for effectively regulating and improving software process metrics, and promoting the mature level of the organization?s process capability.