With quick evolution of grid technologies and increasing complexity of e-Science applications, reasoning temporal properties of grid workflows to ensure reliability and trustworthiness is becoming a critical issue. Relaxed Region Analysis (RRA) is proposed in this work for performance optimization of grid workflow verification by decomposing workflows into separate standard regions with parallel branches. The approach is implemented in GridPiAnalyzer, a Pi Calculus based formal verifier for grid workflows, and validated using gravitational wave data analysis workflows. Detailed experimental results illustrate that RRA can dramatically reduce CPU and memory usage of verification processes.