In this work, the swirling flow field induced by guide vanes was studied using electrical resistance tomography (ERT) and numerical simulations. The results show that the two-phase water and oil mixture moves in the same axial direction for this type of flow field, which is very unlike the flow behavior of a traditional hydrocyclone with a tangential inlet. In the pipe behind the guide vanes, the smallest axial velocity and tangential velocity are located at the center of the pipe. From the pipe center to the pipe wall, both pressure and velocity increase gradually. Downstream of guide vanes, the maximal oil volume fraction is observed at the center of the pipe. From the center of the pipe to the inner wall, the oil volume fraction gradually decreases. Moreover, ERT can precisely show the oil distribution in the pipe section. These studies prove the possibility of efficient oil and water mixture separation by guide vanes, and the results may be very important for guiding the optimal design of vane-type pipe separators.