Mitsubishi Heavy Industries Group provides plant piping and heat exchangers. When designing these products, the so-called gas-liquid two-phase flow phenomenon must be considered. Gas-liquid two-phase flow involves physical phenomena such as phase change and gas-liquid interfacial drag, which do not occur in single-phase flow. It is very difficult to predict or evaluate gas-liquid two-phase flow compared to single-phase flow. We have developed a two-phase flow analysis method based on the two-fluid model and conducted performance and design index evaluations for related products. This article introduces the overview of the technology.