Abstract: The flow patterns of oil-gas-water three phases flow in inverse U tube is studied by experiment via vision combined with the methods of conducting probe and optic probe. Experimental results show that the flow pattern distribution in the vertical parts of inverse U tube is different from that in long straight tube, which shows its own characteristics. The flow patterns of oil-gas-water three phases flow in inverse U tube is very complicated due to the effect of oil/water and bend. Flow patterns map of oil-gas-water is set up, in which oil based and water based three phase flow patterns can be drawn in the same figure.