High-level process management is quantitative management. The Process Performance Baseline (PPB) of process or subprocess under statistical management is the most important concept. It is the basis of process control and improvement. The existing methods for establishing process baseline are too coarse-grained or have some limitation, which lead to inaccurate or ineffective quantitative management. In this paper, we propose an approach called BSR (Baseline-Statistic-Refinement) for establishing and refining software process performance baseline, and present the experience result to validate its effectiveness for quantitative process management.