Steel structures are slender structures, their thickness is small compared to the width. Leading to structural steel is prone to instability. Instability in steel structures is the main cause of sabotage. According to the standard TCVN 5575: 2012, which prescribes steel structure design, the provisions related to instability account for the majority. However, the process of globalization is developing rapidly, the demand for using steel structures in the construction industry is strongly developed, leading to research and study on foreign standards such as AISC, BS5950, Eurocode is very necessary. In particular, the American Standard AISC specifies in detail and there are many design examples that help engineers understand and apply. This paper study on the Lateral Torsional Buckling of the steel I-beam according to Vietnamese Standard TCVN 5575: 2012 and American Standard AISC 360-10.