Two-phase flow is very often found in industry, such as petroleum, power generation, and food. Two-phase flow in geothermal power generation which consists of water and steam mixture is avoided in the piping system since it can damage the equipment in the operating system. Therefore, considerable knowledge of the flow patterns, phenomena and the characteristics of two phase flow is necessary to be taken, such as Computational Fluid Dynamics (CFD) simulation method. This research was done by using CFD simulations method with Ansys Fluent 15.0 software to determine the changes of stratified flow characteristics. The fluid used in this simulation are water and air. In this simulation, obtained changes in the flow pattern characteristics of stratified flow, such as stratified wavy, stratified roll and ripple. The model used was Volume Of Fluid (VOF) by using turbulent flow of k-ε. The variations of water superficial velocity (JL) used was 0,025 m/s – 0,1 m/s, meanwhile, the variations of air superficial velocity (JG) used was 0,05 m/s - 1 m/s. The pipe used was acrylic pipe with a diameter of 19 mm and a length of 1000 mm. The simulations used was 2 inlet, water inlet and air inlet and with one outlet. The results based on the simulation showed that: (1) The stratified flow pattern formed are stratified wavy, phenomenin of roll and ripple. (2) The flow pattern is not constant or changing into forms depending on the superficial velocity of gas or air and the superficial velocity of water and time of data collection. The longer the time taken, the more perfect the stratified flow pattern produced by the flow. (3) The wave frequency of wavy stratified, ripple and roll will tend to decrease when the value of JL is higher, meanwhile, the effect of JG is not significant on the frequency of wave.