Rumex japonicus Houtt (R. japonicus) is used mainly to treat various skin diseases in Southeast Asia. However, there are few studies on its quality evaluation methods and antifungal activity. To establish the quality control criteria for the effective parts from R. japonicus against psoriasis. High-performance liquid chromatography (HPLC) was established for its fingerprint, and the similarity evaluation, cluster analysis (CA) and principal component analysis (PCA) were used to reveal the differences of those fingerprints among the tested R. japonicus. Network pharmacology analyzed the relationship between the components and psoriasis, revealing the potential targets of R. japonicus. Oxford cup anti-C. albicans experiment was used to verify the antifungal activity of R. japonicus. HPLC was developed for the R. japonicus fingerprint by optimizing for 10 batches of quinquennial R. japonicus from different habitats; the 18 common peaks were identified with 10 characteristic peaks such as rutin, quercetin, aloe-emodin, nepodin, emodin, musizin-8-O-β-D-glucoside, chrysophanol, emodin-8-O-β-D-glucopyranoside, chrysophanol-8-O-β-D-glucopyranoside, and aloin, respectively. The network pharmacology-based analysis showed a high correlation between R. japonicus and psoriasis, revealing the potential targets of R. japonicus. The oxford cup anti-Candida albicans experiment displayed a significant activity response to emodin-8-O-β-D-glucopyranoside and the ethyl acetate fraction of R. japonicus acidic aqueous extract. A new and optimized HPLC method was created, and the research provides an experimental basis for the development of effective drugs related to C. albicans. The fingerprint of R. japonicus was organically combined with network pharmacology to further clarify its criteria for quality control.