Inconsistent specification are an inevitable intermediate product of a service requirements engineering process. In order to reduce requirements inconsistencies, we propose PASER, a Pattern-based Approach to Service Requirements analysis. The PASER approach first extracts the process information from service documents via natural language processing (NLP) techniques, then uses a requirements modeling language – Workflow-Patterns-based Process Language (WPPL) — to build the process model. Finally, through matching with workflow patterns, the inconsistencies in service requirements are identified and resolved by checking against a set of checking rules. We have conducted a preliminary experiment to evaluate it. An ATM service case study is presented as a running example to illustrate our approach.