Double-flow phase is the simplest case of multi-phase flows. Both phases have different combination of liquid which move together in flow. Based on the direction of the flow, two-phase can be differentiated into unidirectional flow and counter-flow. This study aims to discover the pattern that occursin a flow in the pipe particullarly to study the bubble flow that occurs in unidirectional flow in horizontal pipe. This study was conducted using CDF software Fluent 15.0 with the water superficial speed was 6 m/s, 7 m/s, 8 m/s, 9 m/s and the air superficial strength was 0,5 m/s, 1m/s, 1,5 m/s, 2 m/s. The pipe used was acrylic flexy glass pipe in which its inner diameter was 19 mm and the outer diameter was 25,4 mm and the length was 1000 mm. The result of the study showed that speed of superficial water and superficial air which formed bubble flow pattern was JL 6 m/s and JG 0,5 m/s numerous small bubbles, JL 7 m/s and JG 1 m/s former small bubbles and with the apppearance of elongated bubbles, JL 8 m/s and JG 1,5 m/s bubbles forming bubbles flow with the length and the number of round bubbles, JL 9 m/s and JG 2 formed bubble which had madium and big size as well with the increased flow rate. Bubble flow toke place because the bigger water superficial speed and its air then the bubbles formed were longer, and if the speed of superficial water and air where small, then the bubble formed would be smaller and larger.