To face the growing complexity of software development and the increasing demand for the software quality, agile practices have been widely praised for their focus on fast feedback, shorter release cycle and frequent customer collaboration. As a typical agile practice to improve software quality and reduce the common risk for software development, Continuous Integration is of high demand to be adopted in the software development practice. Currently, CI (Continuous Integration) is not popularly used in the practice like other agile methods. The implementation of CI process is not well known in the practice. Some agile projects face difficulties to implement CI process in their software development. Vice versa, CI process cannot cover all the requirements from software development teams. This thesis presents a case study on CI process in agile development process, in which the implementation of CI process in the practice and effects of CI process, especially on software quality has been researched with multiple units of analysis. The research results about CI process implementation can be referred as guidelines for the agile projects intending to implement CI. The occurred difficulties to implement CI process and the corresponding solutions from the researched agile projects can be learned from experience by the other practitioners. Moreover, the research results about effects of CI process on Software quality, Communication, Development process and Risk management can give a clear view to the practitioners, what benefits CI can bring to their agile projects. Finally, based on the research on implementation and effects of CI process, a set of optimizations of CI process to improve Software quality have been proposed and validated by the researcher. For both practice and academic research, the optimization proposes are invaluable references.