The Trans Tokyo Bay Tunnel is planned with longitudinal ventilation system equipped with a vertical shaft and electostatic precipitator(EP) stations. Because the tunnel will be excavated in terms of shield method, the EP stations have to be in the tunnel cross section, above the traffic room. The authors have established a theoretical consideration which gives pressure rise effect of an EP station. A simplified model is proposed based on Bernoulli's theorem and momentum theory. Scale model of 1/40 is constructed and experimentally tested. Pressure rise performance is measured under various disposal ratio of the EP station. The result is compared with the theoretical one, which gives rather good agreement except that some discrepancy caused by losses is observed. In addition to pressure characteristics velocity distribution is also measured. After the injection into the tunnel, the high speed region is observed to spread along the tunnel wall.