Spectrum analysis for quality requirements is useful for measuring and tracking them, but current spectrum analysis largely depends on expertise of each analyst. Therefore, it takes a lot of efforts to perform the analysis and is hard to reuse experiences for such analysis. We introduce domain knowledge called term-characteristic map to improve current spectrum analysis for quality requirements. Through several experiments, we evaluated the improved method for spectrum analysis. Categories and Subject Descriptors D.2.1 [Software Engineering]: Requirements Specifications General Terms Requirements Analysis Keywords Quality Requirements, Non-functional Requirements