This prospective randomized, double-blind, controlled clinical trial is designed to address the current challenges in the clinical management of fibromyalgia (FM). We adopt Yangyin Roujin Formula, an empirical herbal prescription used in routine clinical practice, to evaluate its comprehensive therapeutic efficacy and safety in FM patients, including alleviating physical pain and common concomitant symptoms, improving physical function, and enhancing quality of life. Serum and fecal samples as well as brain MRI scans will be collected at baseline and after 12 weeks of intervention. The underlying mechanisms of this formula will be explored from multiple dimensions, including serology, gut microbiota-metabolome profiling, and central neuroimaging, so as to clarify the therapeutic advantages of Yangyin Roujin Formula for FM treatment.