This paper examines an urban rain garden as a case study and evaluates its hydrological performance using the SWMM model. It compares two design approaches—drainage-type rain gardens (RG-dr) and infiltration-type rain gardens (RG-inf)—to assess how design differences influence runoff control, pollutant mitigation, and perceived landscape value. For RG-dr, the mean total loads of four pollutant categories were 56.383 kg, 13.725 kg, 7.484 kg, and 0.904 kg, respectively. Average removal efficiencies for suspended solids (SS), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) were 29.30%, 33.15%, 31.52%, and 39.08%, respectively. Survey results indicate that users were generally satisfied with the visual and experiential quality of RG-dr: more than half of respondents in every age group rated the landscape effect as “good” or “very good,” and over 60% across age groups described the landscape layering as “very rich” or “relatively rich.”