Abstract: Treatment of domestic wastewater is of importance in bettering environment and easing water shortage problem. A new method was advanced to use capillary phenomenon existing in porous medium to filtrate domestic wastewater. River sands were used as filtration media for the laboratory trials with four specially made prototypes of Reversed Capillary Filtration Reactor (RCFR). The purposes of the experiments were: i). to verify the feasibility of the method, and ii) to quantify the effects of the water potential difference in media (WPDM) and the relative dimensional ratio of the diameters of the outer cylinder to that of the inner cylinder wastewater tank (ROI) on the performance of RCFR. Four WPDMs (0.11, 0.26, 0.41, 0.56 m) and 3 ROIs (14/6, 12/6, 10/6) were used in the experiments. Percentage of COD removed from the effluent in the filtration process was used as an index to evaluate the filtration effectiveness of the RCFR. The experimental data showed very good logarithmic correlative relationships of filtration discharge rates and removal efficiency with WPDM values. The filtration discharge rates and COD removal percentage increased with WPDM. At 0.56 m WPDM, the COD removal efficiency had the highest value of about 80%, with filtration discharge rate reaching 0.15 m/h. The ROIs had no significant impacts on COD removal efficiency but clearly had notably inversed influence on the filtration discharge rate, the higher the ROI, the lower the discharge rate. With RCFR, wastewater was under cover of the filtration media, which diminished the emission of bad smell from wastewater to the air environment as well as the swarms of flies.